They are difficult to work on because of their design, some of the power train is accessed from inside the cramped hull and some from the outside. If you don't mind stripping out the radiators, fuel and oil tanks, and the complete engine/trans. assy. there is plenty of room to work in the hull. I have about 25,000 lb. of spare parts so parts for me aren't an issue. I have spare NOS carbs, distributors and 2 complete rebuilt engines, radiators, spare gearboxes, steering gears, suspension and bevel boxes.
There are 14 gear boxes in use to drive one down the road . . . at a top speed of 40 mph.
I have been fighting the "no dry pavement" BS for more than 10 years, it is a myth that won't die. If you put giant sticky radials on one it will most likely break, I've seen it happen to a guy back East, he spent over $5000 in new tires and broke a bevel box. If you measure your tires regularly, rotate them as required, keep the fluids up and don't do anything stupid they aren't prone to breakage. That means no driving over cars, not pulling stumps by attaching a slack chain and mashing the throttle until it pulls taught. They will pull stumps all day with the winch, I've done that and they will do exceedingly well off road because of their ratcheting center differential as they are a TRUE 6WD.
They are a fun truck, I have many photos and videos of ours swimming. I'm getting out of the whole amphibian thing, our M656 and Gama Goat are gone and so will the Stalwarts. I can support just so many toys and we've decided that with the HEMTT, we will drop our MV's to 6 in number (armor + HEMTT). We have other hobbies: kids, V8 motorcycles and haven't completely gotten out of the car thing.
BTW, the guy on eBay with the green butchered one is full of BS, even with the top and back of the cab removed his truck is going to weigh 10,000 lb. more than he claims PLUS they only get 2-3 MPG, NOT the 5-8 he claims.