Vaillant VCW - sine 18 T3 W! Help me keep it alive!

[MrNatural]

Hi guys. My trusty 30 year old Vaillant VCW (albeit lately suffering with intermittent hot tap water, though the heating is fine) has developed a bit of a drip on the left hand side as you look at it. Any ideas? Also today I noticed the pressure was a bit low (about 0.5 on the gauge) so topped it up but stupidly with far too much, sending the pressure up to 3. When I put the heating on water started gushing from what I believe to be the pressure relief valve. I bled the radiators and returned to the boiler to see that the gushing water had ceased and the pressure steady at 1. Phew. Would I have damaged the boiler with such foolishness? I'm not going to try the heating again until daylight tomorrow. Also is there anybody in the Brighton area with experience of these wonderful workhorses that could service it? I would really like to keep it alive. Lot of questions..thanks in advance.
Chris