MZ/MuZ Riders

I own an 18month old Baggy and have done for about 5 weeks now.
I am very pleased with it except for one thing. It has a small oil leak.

After a run oil appears on the underside of the right hand radiator and on the front frame tube below the headstock. The oil is at the correct level and I have replaced the filler cap O ring.

I cant see any oil leaks on the engine or frame/oil tank. The bike is under warrenty but I don't want to drop it off at a dealers untill I know what needs to be done.
I have discussed this with the Importers and had the problem registered with them as a fault.

Any Ideas?

my XT 600 did the exact same thing. the oil fill cap in the frame had a very
small crack, and seeped through it. it was very hard to see.

is the fill cap wet with oil?