I've been doing my best to get through a roll of Kentmere 400 in my Pen F. However, something I noticed at first, the mirror was getting stuck open with the lens that they had on it in the shop, a 38mm f1.8 with sticky aperture blades. I rarely found it to do this after purchasing and having around in the house, whether without a lens, or with the 38/1.8 that I bought for it. I figured it would be good to exercise the shutter/mirror quite a bit considering the age of the camera. Got through more than half a roll (so... 40 exposures or so!) without this happening. However, yesterday I took the camera for a walk in damp, 40-something degrees (f) weather, and the mirror stuck on me four or five times.
I am wondering if the colder weather exacerbated the issue, with old, dry lubricant or the like. I'll have to do a bit of research to find the best way to gently tackle the issue without doing anything major (my analogue repair endeavors have a spotty success rate, I'd rather save up and have someone work on it if the issue is serious).