Also worth checking that the bush is not holding the pipe union away from the crankcase. If a new part, the locating hole may be too tight for the bush, (common on newly plated parts). If an old part it may have previous jointing compound blocking full entry of the bush. The bush may also be too long or not fully seated into the crankcase. The retaining bolt needs a washer and must not bottom in the blind hole, so also check this blind hole for old jointing compound. If the bolt tightens down fully with no gasket in place you can be sure the union will seal against the crankcase with a gasket and a smear of Hylomar.
My parts book for 1949/1953 (Printed November 1953) shows the bush in the exploded view, but it is not listed on Page 15. Later parts book (1954/57) amends this omission.
Chaincase joint width is very narrow, and for a good oil tight seal you need a gasket. Check all the bolt holes for old jointing compacted at the bottom, holding the bolts off the cover. Bad examples require Silicone on the gasket to effect a seal, and as usual check for damaged faces and hairline cracks in the castings. Another source of leaks is the chain slipper adjuster thread. This can be sealed with Loctite but makes the easy primary chain adjustment a little more difficult.
It will be good to hear your story.
Swarfy.
