X300 for £65 is a bargain compared to this!
https://www.gumtree.com/p/video-came...5mm/1279613832
The buffer foam on the Pentax is fine. I replaced the seals and mirror bumper just after I got it. I think it's more the mechanism seizing up. It's working now after 40 minutes on a radiator. If it sticks again, I might put some lighter fluid in the shutter mechanism at the bottom to try loosen it up a bit.