On the Output shaft of that pto was there a bearing,,,or just a bushing??? Probably just a bushing,,,and if there is no seal.. then the screw plate thingy might of held packing to seal it.. packing is kind of a rope type thing that as ya screw down that plate just squeezes the stuff around the shaft sealing it off... or it could have an o ring in the case sealing it off around the shifting shaft... they didnt use to many o rings back then tho... typically its just a bushing and its probably worn out.. A machine shop could make you another bushing but its probably the shaft worn too... i cant tell too good from the picture but it dont look like its leakin that terrible bad..??? do you have a puddle...or just an occaisonal drip..??? A drip you can live with,,unless ur parkin it on the kitchen carpet...hehehehe
