HiCustomer the 560sl was a better overall car but if you're considering a 380sl then an 84 or 85 would be the ones to look at. They didn't make the 380sl past 1985. A common problem was the timing chain guide rails breaking and causing the engine to jump time and damage the valve train. Another problem was oil leakage from the cylinder head gasket due to the threads pulling out of the engine block. The transmission would also tend to leak fluid at the front pump o-ring requiring it to be removed and resealed. Other than that they were a pretty good car overall. Normal wear and tear on brakes and suspension and drivetrain is to be expected just like and other car. If the car has been well maintained to this point I would expect $2000.00 a year on average in annual repair costs. I would not purchase the car without having it inspected by a Mercedes specialist familiar with the older cars. I owned the exact car for many years so if you have any particular questions or concerns just ask me. I'll be glad to help you.
The oil leakage from the heads is visible from underneath better than it is from up top. It would usually leak from the back corner of the head if the threads had pulled out. The chain guides are only diagnosed by a visual inspection. The valve covers will need to be removed for the inspection. A rattling chain for the first few seconds of start ups is a sign that the rails could be broken but if the chain isn't noisey it doesn't mean the rails aren't broken. New chain rails, a chain and a tensioner costs about $1100. A real nice 380sl with a good convertible top could still bring $10,000 but most good ones sell in the $6000 - $7000 range. When you do get it inspected insist that the valve cover's be removed. An inspection should run around $250.00 with a chain rail inspection. Don't buy it without the inspection! Let me know if you think of anything else you want to ask.
I believe you can choose your expert when you post a new question and it will lock the question for awhile to give me time to respond but I've found the best way is to simply request me in your actual post. I'm online quite a bit so chances are I'll see the question. You can also just reply back to this question.