The engine is an OM621.912 engine, something like 1988 or 1998 cubic centimeters, though the letter designation is only 1900 cc. The model and serial number for the engine is located on a metal riveted plate on the block below the cylinder head, left side at the rear. The VIN, as you probably already know, is on the top of the radiator support next to the hood latch. When ordering the parts, you will need both the engine and chassis serial number. The engine may have been changed along the way somehow, so the serial number is a necessity.

The smaller letter "c" on the 190Dc stands for version c of the 190D model. The 190Db was the old pontoon body style. the 190Dc came out in 1961 and ran till around 1966, when the 200D replaced it with nearly the same body but other mechanical upgrades.

The dealer should still be able to look up parts on their EPC, and if they can't, they probably just don't care to mess with something that age.