People have said on here that when trying to put a new oil seal in a rear seal retainer used on the first years of Cubs, the seal fits too loose in the retainer.
Your Cub is a 1975, I guess, which is one of the newer Cubs.
I think they have said the seals fit better in those retainers.
You could try a new oil seal in your retainer, and see if it fits tight. It has to fit tight to not leak around the OD of the seal, and so it doesn't fall out of the retainer. Which means it has to be hammered into the retainer.
Below is a new seal at TM Tractor, you can look at the pics. It says it is a Case IH part.
http://www.tmtractor.com/new/en/365fp.htm
If it doesn't fit tight, then I would buy a used retainer with new seal from tst, here on this website. He repairs used retainers, and bores them out so a new slightly bigger OD seal fits in the retainer.
You can send him a PM.
Tighten the 3 bolts at the rear of the oil pan gently, they thread into the rear seal retainer. The retainer is soft metal, and threads can strip.
If you have an original clutch in a Cub, and it is still good, people on here have said to not replace it.
They have said the original clutches are better quality than some of the new clutches available today.
I remember reading someone put in a new pressure plate, and probably other clutch parts, he used the Cub only a short time, and had clutch problems.
He looked, and one of the clutch fingers had bent down. He thought the metal used in the finger was too soft.
He had to split the Cub again, and replace the clutch again.
You could check the ignition timing with a timing light, and see if it is set right.
It should be set to the TDC mark when the engine is running at slow idle speed, which is about 500 RPM.
It should be set right so it will start and run good.
