Fix my cuckoo-clock?

I own a 130 year old German cockoo clock with, I have been told, a good movement. It currently has three problems:

1. It stops ticking for no reason that I can work out. Very often this takes place after 5-10 minutes, but can sometimes happen after several hours;
2.To get it to tick regularly the clock has to be mounted on the wall at a 5-10 degree angle to the left;
3The clock is currently gaining cuckoos ie if it cuckoos at three,say, on the hour,as it should, after a day or so that number will take place on the half-hour so that the clock cuckoos once at 4, at three o'clock, and 4 times at three thirty. I have tried taking the weight off to allow the clock to catch up with itself, as it were, but this only lasts for a few hours then it once again gains the half hour. The clock has been well serviced over the years (re-bushed, oiled with new chains fitted) so what is the problem?