I recently bought a Zuiko 135 mm lens on ebay- lovely condition, but the lens lock button did not spring up to lock the lens. As the lens was otherwise fine, and the seller offered to refund my money (it was a bargain) I decided, with some trepidation, to see if I could sort it out myself. I have never attempted to repair a lens before. I thought that the spring controlling the button must be either broken or misplaced. I undid the three screws at the back of the lens, fearing that all kinds of small parts would immediately spring out. None did, and the problem was immediately clear. The spring was absent. As it looked as though the lens had never been dismantled, I concluded that the spring must still be inside, so turned the lens back end down, and gave it a little shake. Out popped the spring! It wasn't immediately clear how the spring had been fixed. It had two holes, but I could only see one small pin on the plastic inner surface which might have held it. Closer inspection showed that the other pin had sheared off leaving almost no trace, but in any case, the spring attachment plate was set quite snugly, so did not rely on the pins to brace itself when the button was pressed- they just held it in place. I repositioned the spring over the remaining pin, and fixed it with a tiny drop of superglue. Result: Delight. I could feel the stern face of my Swiss watchmaker grandfather beaming at me from tiny screwdriver heaven!

I hope this helps someone out there.....