I have one of the above, bought for a pittance from my club, that I use for prone shooting. I've been getting the occasional click, lift the bolt and re-cock and it fires the round. The striker runs the length of the bolt with the bolt handle cam operating on the end of a long lug on the striker. I've cleaned crud out of the assembly but have noticed that either several mm has worn off the cocking lug or someone has "eased" it for smoother cocking.
Can anything be added to the end of the cocking lug on the striker to return it to it's original shape? This would mean the striker would be further tensioned against its spring giving a better strike and also allow the safety lever on the back of the bolt to function. Recon its about 3 or 4mm shy as it stands.