If you love the R/C107 Mercedes as much as us then check out this buying guide we came up with.
Disclaimer* We are definitely not professionals and this is just for fun.
The first thing you want to do even before really looking the car over is fire it up from cold and see if the idle is working properly. The car should start up and go around 1400-1500 rpms and after a few minutes drop it's way down to 5-600rpm. I've seen some older 450sl with K-jet take almost 5 minutes to drop down to a proper idle after running up to almost 2000rpm.
Now put it in reverse and listen for clunking or wheel spin. Reverse is the first gear on the shifter.Then do the same thing for drive. If it goes in smoothly that's pretty good. If the gear shifter is very loose in reverse or other gears feel a little bit out of place than the car is going to need gear shifter bushings most likely.
The next thing to look for is if the car has the crap chrome wheel lip arch. These are usually drilled into the car and cause the arch to rust badly if you don't live in a desert. Run you fingers behind the inside of the arch lip if it's rusting bad you should feel it watch out for sharp screws. Now check all the rocker panels and in particular the jack points for rust and rot.
Look carefully behind the front wheels at the body of the car for rust and rust holes. These cars are very prone to form rust holes here. Check around the gas tank door for rust and around the bumper mounting points for rust. Take a good look at the paint on the the gas area many times if the car has been painted you'll find evidence here.
If you don't mind getting a bit dusty crawl under the car and look at the rear differential for signs of leaking, you should also be able to see the flex discs and if they are dry rotted (usually the diff is leaking a bit and the flex discs have dry rot). While you're at it take a flashlight and look at the fuel line going into the fuel pump it's located next to the passenger rear tire under a black cover usually. Sometimes the cover will not be there in which case it will be sticking out at you.
Now crawl under the front of the car and look for leaks. Usually something is leaking I wouldn't get too bent out of shape. On these cars it's a matter of how much is it leaking. Some oil consumption is normal after a thousand miles due leaking valve seals on many of these m117 engine vehicles.
Paint and body work is expensive try and buy a rust for example when possible. The nicer the paint job the more money you can spend on other things like getting the car running correctly.
When the car was made it came with a factory hardtop and soft top. If the car has the original factory soft top then you can assume it's going to need to be replaced unless you plan on putting the car in a glass case. Many times the hardtops are lost or switched most hard tops have the serial number stamped under the bottom lip. It's nice when these match.
If the soft top needs to be replaced along with all the soft top seals and window seals you should plan on spending $2,000 to $2,500 using decent materials. If the windows are damaged then the entire top should be changed those window repair kits have never worked for us.
Now start the car and let it warm all the way up to 80 plus degrees Celsius. Once the car is all the way warm take it for a nice test drive. Check the oil pressure at a stop light with the engine at full temp, if it's dropping to between 0 and 1 then that's something to consider as a tired engine.
If the car overheats before you make it around the block that's not good.
Many times the thermostats stick open after the cars sit. If the car doesn't get to full temp it will need a thermostats, they are very cheap.
Make sure the car makes power under a load, on the freeway doing 60mph it should be fine.
Now for the interior try and move each seat back and fourth. Check for all the chrome trim pieces on the seats, each seat has 4 pieces 2 on each side. Test the door locks and windows. I would expect sun damage to the wood trim and a cracked dash. Check the coolant for signs of oil.
Suspension wise parts are DIRT cheap. If it's a keeper the steering coupler and damper will need to be replaced, probably the shocks, ALL the tie rod assemblies, ECT.
Look at the brake rotors AFTER you drive it they should be shiny if one or more isn't you will be replacing a caliper or more. When sitting inside the car check the under dash covers are present one both sides, then look at the courtesy light for signs of melting or damage. Next open the glove box and look to see if it has the grey liner in the glove box with the light many times these are misformed or gone.
After the car is warm with the engine running pull the dipstick on the transmission. Most of these cars seep transmission oil when they sit it's very common to see the car down a quart if it sat for a long time, usually it needs to be topped off.
When you go under the car take a small ball hammer or a screwdriver and tap the floor pans neither should be able to pierce it. If you do then there is a lot of rust to repair. The floor pans love to rot out. Also look at the fuel and brake lines these cars are all at least 30+ years old at the newest many times fuel lines will be ready to crumble due to dry rot.
Usually the grommets for the latches on the top of the windshield these are missing as they crumble eventually, these are very cheap to replace and make the tops seal properly.
If the car does not have a hardtop they are interchangeable on the R107 and usually can be bought for $500. Get a storage stand for the hard top it makes life easier and it prevents damage.
This is a basic buying guide for a daily driver type car, if you are looking for a concourse car we have about 100 more items to look at. Now get out and drive these wonderful cars.