I'm going to push some tough love onto mate, so don't take this the wrong way.

Devil's advocate: No, I don't think you should get one.

The reason why was your statement here:
Manual schmanual. That's no good. Have you looked at the manual? To even get a good baseline, you'll need to poke around the engine in ways that will make things become pretty big and "mechanical". Especially when it comes to troubleshooting components like the fuel system, vacuum leaks, idle issues, and more. Take a look for yourself: https://www.startekinfo.com/StarTek/outside/11883/?requestedDocId=11883

Now this all changes IF and only IF you have tons of disposable income that you don't mind throwing away.

Why? Because these are very very needy cars.

"But Beast, I'll just go and buy a low mileage one instead!"

Ah contraire my friend. Low miles on these cars don't mean anything anymore because age has now done the most damage. Rubber components will need to be replaced, hoses get old, air leaks get in, and these engines (all of them) get very very cranky when they aren't driven often.

Most likely, any car you purchase will have had some idiot mess with the air metering screw attempting to hide the aforementioned issues above. This will not fix anything and will aggravate the problems even worse, putting extra strain on other components requiring even more fixes!

Even cars that come with mountains of receipts done at the dealer mean absolutely nothing. I'm living proof that dealers can do very shoddy work. I had to teardown the top end intake on my 380SL to remedy a fix done by a dealer here in SoCal about 8 years ago by again some grease monkey who didn't read the manual and use some sealant where he wasn't supposed to.

You can avoid this by purchasing a better cared for car that a forum member here or on Benzworld has owned and loved for years. You might avoid the fix it monster, but you will one day run into some issue that might take more troubleshooting know how that a mechanic these days won't know how to do.

So you have a problem and don't like the idea of feeding a smoke machine in to find where the air leak is or don't fancy the idea of disconnecting fuel lines to do pressure tests on the various systems.

What will most likely happen is if you aren't 100% proficient in the systems that are on your r107, a mechanic will throw parts at the problem at your expense. If you're wealthy and don't care, then have at it. If not, you will see a car you spent $8-10k on balloon into a $20k car.

Ironically, these aren't complicated cars. The way of troubleshooting and maintaining them has gone out of style and thusly leaves the average mechanic up the creek unless you can find a good one. I've had better luck on slots in a casino in that regard.

But, even if my warnings haven't swayed you, here is what I will tell you to look for:

All R107s prior to 1985 are affected by a defect in the subframes. If this hasn't been remedied with the gusset reinforcements, it isn't a matter of if the crack will occur, but when it will occur. Look at some of the pictures around of what that failure looks like. It's a catastrophic problem that you don't want to have happen when driving! Post 1986 models have been fixed and won't have this issue.

Prior to 1976/77 (check I don't know), engines have the DJet injection system. It's a very efficient early style fuel rail system. However, it relies on 70s technology and can be a mess to short correctly. I don't have experience on this so good luck.

R107s made after 1986 start slowly including various computer diagnostics into the works which can be helpful in determining faults. 1988 and 1989 MYs have a rudimentary blinking code system that can be used to determine issues.

1977+ cars to 1985 have the KJet injection system. It's simpler, but is very sensitive to air leaks that will need to be hunted down and fixed if you want a properly in tuned vehicle.

Avoid any cars that haven't had the following (or budget for the expense).

1. Cars that have not had the subframe fix done.
2. 380SLs that haven't had the double chain timing rough conversion (84-85 came from factory with the dual timing chain).
3. Ask the owner what the fuel economy is on the highway. Obscenely low numbers (15 and below) are indicative of engine issues.
4. Cars that have the evil automatic climate servo (ACCII). Google around for what this looks like. Easily identified by the panel https://image.isu.pub/180411232051-c3bac3660dd22e9eee51ca01ddd69586/jpg/page_1_thumb_large.jpg


Not trying to be a negative nancy, just trying to paint you the full picture of what you're getting into.

Hope this helps!

__________________
-Typos courtesy of my mobile phone.