The mirror linkage in Pentax cameras runs dry. At least, service manuals don't call out any lubrication points. If they are sticking the solution is disassembly and cleaning. Any latch points or high friction points are lubricated with grease. Generally, only points that are involved with the release of the shutter are oiled, so curtain rollers, curtain wind gears, high speed cam, etc. The mirror return gear on the bottom of the camera can also be oiled because it is directly linked to the closing curtain but you should disassemble it and clean the shaft first.
Nyoil is a good one to use.