Ran to the store, 20 mins later come out, put my seat belt on, but it doesn't buckle/click/hold the seat belt. Couldn't get it to work, so I drove home buckled into the passenger side.

Got home fiddled around with it, and I noticed if I barely push down on the release button while I hold the belt in the buckle, it'll spring out and catch like it normally does.

A quick search on this and the W203 forum revealed no previous postings. Anybody had this happen to them before? I wonder if something's broken inside the buckle itself, yet for some reason it still works if I barely push it.

Hmm. Odd. It may sound silly but I would start simple first and spray some WD40 into the slot and see if that helps loosen up the mechanism.