I had a Kar98 that was the same way and it turned out, as near as I could tell, that someone had over buffed the cocking piece where it engaged the sear thereby shortening it ever so slightly. (the whole gun had been over buffed before it was re-blued)
I dug through my box of Mauser parts and found a CZ cocking piece in good shape. It fixed the problem. So, the cocking piece is the first place I would look on this Mauser too.

Al