I've driven quite a few of both. The diesels are great and I started with them back in the days when most gas engines still had carburetors. Compared to a carbureted gas engine, a diesel Benz will outlast it by a wide margin. An injected gas car is a totally different matter. As far as engine longevity goes, the injected gas engine will last about as long as a diesel and if it is has the same number of cylinders it will usually be less expensive to repair/overhaul when the time comes.

As far as the 95 SL goes, it has an M104 engine which is a good engine. The head gasket reputation it has is a bad deal, but this does not mean that EVERY 104 engine will need a head gasket at a given mileage.

Good luck,