WH401, why should he or anyone have to figure out a way to rig something that is obviosly a poor design OR a "one off" malfunctioning piece. I don't think any of us payed the thousands of dollars we paid in hopes of figuring out ways to make our equipment perform their intended tasks. Why can't folks just help solve problems instead of making judgements concerning another person's experiences or wishes? I can assure you that I would not put up with his situation either. And just suppose that he comes up with a a way to fix it and his way allows it to happen again and it damages the tractor or mower......then what? The warranty is out and he is left paying who knows how much to fix something that should never have needed to be fixed in the first place!
Troy
First off, if you search TBN you will find that the many other owners of 2320 - 2720 tractors that are equipped with the 62D mower decks aren't having this problem. That itself shows that this problem is unique to only his tractor and just a "poor designed" piece as you may think.
Secondly, if he bends the end of the cotter pin, or attempts at using a threaded bolt in place of the stock bolt, or simply just bends a wire through the end of the bolt hole, how is any of that going to damage the machine? Most likely there is a lot of clearance around that moving part anyway and none of these things would do anything to hurt the tractor. Even if some how they did "damage" the machine, I doubt if it would be more than a slight paint scuff. Possibly it could bind the linkage where the deck lifts up towards the machine, but that would be something you check out before you go mowing for the first time.
Thirdly, I'm offering my opinion because the OP wants to take, and possibly sell, a perfectly good, no problems what so ever tractor, just because of a cotter pin falling loose from the mower deck assembly. I'm in no way trying to be rude or give the impression that I'm trying to talk down to anyone, but a problem such as this is about as minuscule as they get and shouldn't be the basis for such drastic action. Sure the OP, myself, and many others on this site have paid thousands of dollars for these machines, but being that this problem isn't a huge operational nightmare, there is no reason one couldn't improvise to fix it. If the tractor had electrical gremlins from day one, or the engine kept cutting out, then yeah, that would be an issue to trade it for, but not for something like this.