On your oil filters. They are both designed to be cleaned and reused. Often you will find the sump filter torn. Easy fix. Is small tear just clean really good, coat with JB Weld or your favorite epoxy. If large tears or chunks missing cut a patch out of an adult beverage can that covers the hole from the steel top and bottom and out past the hole a bit and glue in place with the epoxy. Once glued in place and dry another coat on any iffy spots.
If you can find one an extra sump plate, sump filter and side cover filter can be handy. When doing an oil change just swap the dirty parts for the clean ones. This speeds up the oil change and you can clean the dirty parts anytime.
As mentioned the countershaft nut could be loose, many have found it to be barley finger tight. A leak there is generally not the seal. The nut pushed the sprocket against a spacer that passes through the seal and presses up against a bearing race inside the tranny. Oil is under pressure from the oil pump to all the bearings and shift fork parts inside. If the nut is loose oil passes between the bearing race and spacer, along the splines on the shaft, and drips out between the spacer and sprocket. Tighten the nut up seals off this oil escape route.
You clutch pushrod seal just ahead of the sprocket is much more apt to. Leak than any other seal in the engine. It not only can spin but slides in and out of the seal. This can drag dirt into the seal,
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