The 380s are the least desirable of the 107-body (72-89) SL cars. They are prone to comparatively early timing chain failure (very expensive) and the threads in the aluminum blocks tend to strip when the heads are removed. The timing chain can be converted to a stronger double row type, but this is also expensive. While the car you describe has low miles and will therefore probably not need major attention for a while, the 380 only had 160hp, which makes for a, uhhh, leisurely acceleration rate. For the price this seller is asking, you could get a later 560SL with higher mileage, which is a better car in every way than the 380. A late production 450SL could be had in excellent condition for less money as well. If properly maintained, the 450s run forever, and the body style is virtually identical to the later cars.
If you have your heart set on this 380, DEFINITELY have it thoroughly checked by a shop that specializes in Mercedes. Any old mechanic will not be familiar with the problem areas specific to this car, and could miss things that you should know about before you make a final offer. Good Luck and enjoy the car if you buy it.