Looked at a 98 C280 with about 74K miles today (buying), and started it and let it fully warmed up. Shut it down and then tried to start it again and two times in a row it would only turn over two times then it went dead (don't remember if the lights in the dash went out or not). On the third try, it started fine and we took it for a long test drive (to charge what we suspected was a weak battery-sitting for a while at a car dealer). Return, and tried restarting it after turning it off (test the battery) and several times it would crank just two times and then dead. After a few tries, it did crank until it starts (about 3 turns). sometimes normal, other times just two cranks and it's dead until I try again. It has a MB battery, so I suspect it may be the original (most buy the aftermarket because of price I guess), if so perhaps it's just old and weak. However, I don't know if there are any inherent or common probs with sensors or starters that would give the same symptoms when the engine compartment gets hot which is the main question I have here.

Any ideas?
TIA MarkC