gas tank leak

I recently bought a 1987 VW Cabriolet with a few known problems.

The most immediate is that the gas tank "weeps" when more than 1/2 full. The gas tank holds pressure and the amount lost is not significant (except for odor and environmental considerations).

I have seen pictures of the tank and think I see 3 holes for Filler, Sending Unit and In-tank pump?

I do not yet have a VW repair manual... recommendations?

For completeness:

1987 VW cabriolet
4 cylinder gasoline
5 speed
"stock" everything

There are a couple vent hoses that could be bad. There is alos an access cover under the rear seat that you can check the level sensor & pump cover plate seal.

Very helpful... thanks... I'll get a manual and start digging around. The last owner was fairly handy but could have missed something obvious anyway...

Thanks,
- Steve