First of all, what Tim told you is absolutely wrong. You do NOT have a DB of JDB pump with a separate shaft with umbrellas seals.
As to that fuel shutoff - no -it has nothing to do with fuel in the oil. Those shut-offs were a common problem. Often, the little shut-off plunger would stick. So, it got yanked out and thrown in the garbage along with the spring. Then, the machine ran fine, but you could not shut it off - you had to stall it some way - or turn the fuel off at the tank.
Those shut-off solenoids have not been availble new for many years. If you found one for sale, it is either new-old-stock, or it's used. I've given many away to people on these forums, but I don't think I have any left. I worked in a Deere pump shop for many years. Some pump shops now are repairing these pumps with all used parts, but most won't touch them. If you don't have used parts to use, there's not much you can do.
That pump comes off the tractor with the shaft still in it. It uses a conventional, self-contained oil seal, not a set of umbrella seals like the DB or JDB pumps use. To replace that seal - you do NOT remove the shaft. You simply remove the front cover from the pump. That cover has the seal pressed into it. Change the seal and put the cover back on. Then, reinstall that pump onto the engine.
If you had to spend any real money on repairs, you'd be way ahead to use the Deere changeover parts and install the JDB pump. All parts are availble for that and it is still made new.