Saunier Duval SD 620F Leaking?

Hi Folks, I have been looking after my old SD boiler for twenty odd years, I have replaced hoses, pump, fan, and encountered a multitude of faults, but this is a new one on me. After a service yesterday I started getting water dripping from behind the temperature/pressure gauge. I removed it and cleaned the surface behind re-fitting it with some sealer around the area where the pressure gauge pipe goes into the boiler. Amazingly it still leaks and I have collected a good couple of pints overnight. I have been online looking for spare parts without success. Can anyone give me some advice, or knows of a good website to checkout. I am looking for new gauges which I understand will come with a seal, I am hoping this will solve the problem. Many Thanks.