The early USA version 104's had an additional idler sprocket for the timing chain. That's why they're noisy compared to later versions. They also used the LH-SFI engine management system. It's not a bad set-up, but IMHO, the HFM-SFI system (with resonance intake manifold) is far superior in terms of performance, reliability, and ease of diagnosis.

Here at the dealership, I don't see many early 104's anymore, but I don't recall them having any major engine issues. The 103's were the last of the oil burning,valve guide wearing,camshaft eating MB engines. Headgaskets of course, are another story.