A little up/down/sideways movement at the front of the transmission shaft is normal, that's why there's a pilot bushing in the crankshaft. Oil leakage isn't, unless it's just a tiny seep. Some SM-420 transmissions have an oil seal built into the front bearing retainer, while older ones just have an oil slinger and a drain hole to return any lube that gets past the bearing to the case. Pull the retainer (carefully) so the needle bearings between the input and output shafts don't fall out, and check to see if there's a seal in there. If not, be sure the drain hole back to the case is clear, and the retainer drain hole is aligned properly with the hole in the case.
Jerry
