My first 2415 repair

[boxygen]

I was working on my snowplow subframe yesterday and I noticed the backhoe pins had stress on them and wouldnt come out without some hitting them lightly with a hammer. They normally can me taken out by hand no problem. I traced the problem to the rear of the tractor. There are 3 drainplugs for the transmission (HST) and rear end, one almost dead center of the tractor and two on each side under the rear axle. Two pieces of tube steel make up the BH subframe that travels under the tractor and connects to the loader mounts up front. Each of them are right underneath each drainplug for the rear end. There is only about a half inch of clearance between the drainplug and the subframe and the left plug loosened up and backed out against the subframe. I did a bunch of digging with the backhoe last weekend and the tractor sat in the garage all week. Even with the drainplug backed out there was very little leakage and fluid level was normal. A little on the subframe, but not enough to even make a puddle on the concrete floor. Wishful thinking, I dropped the backhoe to tighten the plug. Of course it tightened but was for the most part stripped. I think using the backhoe put pressure on the threads for a while because there is some movement on subframe while in use. I consider myself very lucky that I had the backhoe on when It loosened up. I could be buying a HST right now if I had not. I'm not that worked up about it actually but I need to fix it. I assume the best option is drilling and tapping for a helicoil or equivalent. I backed out the plug a little bit more and the threads on the bolt look fine. Is Helicoil my best option? What have others done?
I consider myself pretty diligent about maintenance and checking bolt tightness but this enforced that there is no such thing as too much checking. Thanks in advance for any advice in the best repair. By the way, there are about 170 hours on the machine at this point.

[driver444]

I would drill and tap to the very next available tap size, and use a fine thread bolt with a washer for a plug, (even if it's standard and not metric). Leave as much of the original casting as possible in case you mess up. In other words, I wouldn't start out by drilling the hole out to accomodate the Helicoil as a FIRST resort. That's usually a couple sizes bigger. You can always drill out more, but ... you get the point.

If that doesn't work, and you do have to Helicoil it, Use some type of sealant on the coil when you screw it in to avoid leakage between the threads. If you do what I said and try the first suggestion, and it doesn't work, there should be plenty of casting left to go with the Helicoil.