On a related matter, despite having all new washers, o rings and disc, my tap kept weeping from the joint between the bowl and the body. Turns out the filter disc was slightly dished when viewed from the side, so the centre bottomed out before the outer rim. This prevented the disc and the Oring from seating against the body of the petcock,no matter how tightly you did up the bowl. Of course, with the tank on the bike you have no chance of seeing what's happening, only when it or the petcock are on the bench can you see what the cause is. Just flatten the filter disc and ensure both the centre and the rim seat properly.