Fuel leak after not being used for 3 or 4 days

[toolsntat]

2L 1980 Aircooled stock engine and system.
Did read the Wiki post that's up.
Odd situation, petrol will drip off bottom of engine on initial start up after not being used for a few days.
Does take a bit of cranking to start up.
After a very short time, maybe 2 or 3 minutes with stop and start it won't leak.
I thought it was the fuel pump (manual) and pulled out the drain (?) pipe to see..... nothing.
Can a faulty fuel pump initially leak and then seal when pressurised/wet (from petrol) ?
I'm hoping a new pump (in post) will sort it out but just wished I could actually see it leaking to know for certain.....
Cheers, Andy

[toolsntat]

Lifted from the Glastonbury thread.
Perhaps this might be the problem I'm having.
@silverbullet

Your fuel pump might be past its best, eg if its one-way valves are not sealing. A good one will hold fuel up for ages.