Vauxhall Corsa Vegas 1.4 (1996) - Rocker cover oil leak problem?

Hey,

I recently noticed my car was leaving small puddles of oil and upon further inspection discovered it was coming from around the valve (rocker) cover. I bought a new gasket (cork replacement from Halfords) and some of that silicone paste stuff, used a gasket scraper to clean up the head of the engine so it was free of any muck. I also checked the hoses attached to the rocker cover for any blockages, and cleaned up the oil cap itself.

I noticed when i took the rocker cover off that there was no gasket in place! I think a previous owner had used some sort of instant gasket which had perished.

I carefully positioned the gasket, loosely tightened the bolts down (replaced some washers too as some had snapped) on the cover until finger tight. I haven't got a workshop manual so don't know what torque settings the valve cover bolts need to be, so I just gave them about 1 full turn and some little tweaks until it felt reasonable. I gave the silicone sealant time to set, cleaned the oil off the head and then ran the engine.

The problem - the gasket seal seems to have worked and no oil coming out here! BUT, oil has started to seep out under the bolt-heads holding the cover down. I don't want to overtighten them and ruin the cork gasket which appears to be holding.

I checked the oil level, topped it up slightly and took the car for a run around to get it warmed up. When I got back I saw that more oil had seeped out from under the bolt heads.

Has anyone else experienced this problem? Is it worn bolts, or are they not tightened up enough? I've checked the hoses, but could too much pressure be building up because of some other problem?

I don't really wanna take it to a garage if i can help it.

Its not majorly leaking, but its not a minor seep either so I'd like to get it sorted if possible.

Any advice on what could be causing this?

Cheers! (sorry for the long post)