Inability to shut one eye - anyone else?

I too have the same problem not being able to close one eye but I dont have any trouble focussing. Have you thought of getting an eyecup? they work really well. If you want to go better this is a gadget on the market, I cant remember the make but its similar to the folding sides on top of the TLRs, If you have the joy of having Live View on your camera thats also another option