Sometimes the caps can crack, usually from being over-torqued when screwed on. (Power-Pole has this issue also; I had to replace a cap cracked by someone other than myself.) I haven't experienced an oil leak like yours, but I would think that a cap just not quite tight enough might develop pressure but let some oil get past the gasket seal, or past a bad gasket seal even if tightened to specification.
The first thing I would do is inspect the gasket. It could be damaged from age or over-tightening. You might try flipping the gasket over to improve the chance of a good seal. If the leak stops, get a new gasket. Inspect the cap housing for cracks.
Edited by Flippin-Out (04/24/16 08:36 PM)