Welcome to the forum!
Hmm. Lets see.
Well, I think I would stick with the $1800-$2200 offer on this car, considering it has the transmission leak. It could be as simply as a pan gasket, or something worse.
Like Gigtimes said, the A/C could run into big $$$ to repair, but if you live in a cooler climate, this is not a cause for concern. If you live in the south, that may be a different story.
The hard starting sounds like it may be out of time or something. Weak fuel pump? I am sure someone with more knowledge about Mercedes cars will key in on this one. Is it is northern car? I know you said "rust free" other than one small spot, but if is it a northern car, be sure to check out the undercarriage and rocker panels. I have seen a lot of these cars from up north on Ebay, with rust issues.
Many times the exterior will appear to be in glowing condition, but rust can lurk underneath the chassis.
Also, depending upon what type of "front end" work is needed, that could also run into $$$ to repair. Before you know it, you could have $$$$ more sunk into this car.
I know what you are thinking,
, because I have been where you are- looking for a 80s S-Class Mercedes. I have looked for a older Mercedes for years, until I recently took the plunge and bought a 1985 Benz. I had question after question here, to the point where some were disgusted with me and all of my stalling and questions.
I was just afraid of making a mistake and buying a costly lemon. That would never do!
I bought mine so cheap that it really does not matter and luckily, it seems to be a very good car (so far).
Good luck with your purchase!