I've used alloy sump plates on a number of bikes and they are great since they allow easy draining of oil from cases and the drain bolt often has a magnet to catch any fine metal particles.
If you're finding a drop of oil on the end of the drain bolt, the cause is often from leaks in other areas which slowly accumulate on the bolt. I would check the following areas for leaks & weeping oil:-
- the alloy sump plate can itself leak especially if the 4 studs/bolts aren't secure or stripped. Make sure the threads into the crankcase are in good condition, helicoil if necessary. The gaskets between the sump strainer can also leak so best to use new gaskets and a tiny smear of sealant as well.
- leaks from the oil manifold, timing side cover and other areas can all end up as a drip on the sump drain plug so check carefully for the source.
Regarding the type of sealing washer to use with the bolt, I would choose copper first followed by fibre washer. You don't need to use much torque
to secure the bolt, no more than about 20 lb/ft otherwise you will end up stripping the thread (like I did) in the soft alloy sump plate. Luckily I was able to tap out the thread to the next oversize and fit a larger sump bolt which are readily available.