try this before you split the cases, get hold of some gel type superglue,drain the gearbox oil and remove the inspection cover, then degrease the seam on the inside of the crank cases (this is where the oil may be drawn in) from the top down to the drain plug, i used strong paint thinners, then treat the seam with some superglue activator.
let it all dry out then squirt the super glue at the top of the seam with a big enough blob and watch it slowly run down to the bottom, then squirt this bead of super glue with the activator so it goes off.
repeat if neccessary to attain a good thick bead (i did it twice).
the glue will be pulled in by any gaps and will then seal with the activator.
this is only a temp fix but works well and cured an air leak on my twinport for a whole season till i had time to split the cases and use the old silk thread trick.
dont worry the cases will not "super glue together" as your just sealing the tiniest of leaks you just scrape it off when you split the cases.
