I thought I'd resurrect my late father-in-law's 1930's Enfield mantel clock which has been in storage for many long years. Happily the clock runs, it keeps good time and it strikes on the hour and the half hour, but there's one problem. The clock strikes the hours correctly except at midday and midnight, when instead of striking 12 times, it only strikes 11. I don't have much experience at clock repair, but I'm reasonably capable and willing to have a go at most things. The clock isn't worth much and I doubt I can afford a professional horologist. Is this problem resolvable and is it something a novice could tackle? I would certainly appreciate some advice as to the probable cause and guidance on tackling it. I have included a couple of pictures and there's a link below to a YouTube video showing it working (striking six). Thanks for your help.