Thanks guys, it's an automatic with the leak at the transmission. I've eventually managed, after an afternoon on the web, to source the bolt from the US. Postage is more than the bolt, but never mind. Can't source the seal anywhere but will get the old one off and see if, as suggested, I can get something I can use from a hardware store. Good suggestion re the pressure, let's hope that's not the problem as that sounds like a big job!