The Pentax LX sticky mirror syndrome is a well-known problem. It is a known phenomenon that LX's mirror rest will become sticky with age, hence will delay shutter firing.
I have adopted a simple solution. Two very small pieces of adhesive velvet where the mirror touches the rests not only prevent the mirror from adhering to the sticky rests but also compensate (with its thickness, less than 1/5 of mm) the slight lowering of the mirror. The two gummy rests with age become sticky and loose elasticity. Under the pressure of the mirror the rest loose their shape and thickness (this is negligible with a new, elastic, rest, but not with this sticky old gummy things.
The procedure is pretty easy.
Mirror up, place the camera with the back on the table, and locate the two mirror rests: one is on your left (it is square) the other on your right (it is a cylinder). Put the adhesive black velvet as shown in he two macro photographs (taken with a Nikon D200 and a Medical Nikkor 120 mm) and the sticky mirrors problem has gone, not forever though: a more definitive solution is to have the camera serviced because the LX has some dampers also inside the shutter mechanism and for this s professional is a much-needed help. However, if my suggestion solves the problem give it a try.
Left side of the mirror box (to the right of the observer) with the cylindrical rest.
Right side of the mirror box (to the left of the observer) with the square rest.
