The only thing we really kept playing with in the engine was the clutch. We tried two styles of Hinson setups (four-spring and six-spring), and they were both very solid but didn't offer a huge difference over standard, and plate wear was similar as well. We did have very good luck with a Barnett Dirt Digger clutch kit that outlasted stock and had a better feel due to different springs. We also spent a fair amount of time with the Rekluse EXP and Core clutch on the bike. The EXP anti-stall was incredible for those who liked it, and the Core clutch was good as well, but both of the Rekluse setups take a bit more attention in setup and tuning to keep them on top of their game. For exhaust we spent most of the year with the Pro Circuit system on the bike, though more aggressive riders preferred the Yoshimura system. A few preferred the stock pipe or, for even smoother, quieter and more mellow delivery, an FMF Q slip-on muffler.We went through a few sets of brake pads, replaced with stock Honda parts once then with Renthal pads which gave the bike a bit more grab at the cost of slightly quicker wear. The chain and sprocket was replaced with a Renthal TwinRing sprocket and Renthal O-ring chain, so we would not have to worry about it again. The sprocket initially dished the steel teeth but then never showed much wear after that. The chain only needed adjusting twice. We've heard of some riders having issues with the fuel filter inside the gas tank on the pump getting dirty and clogging, but ours was not dirty at all.About halfway through the year we ordered a fresh set of plastic and matched it with a RidePG.com graphics kit to make the bike look like new again. Of course, since I was riding it the most, it was my number. The kit was still looking good 70 hours later.The way everything was still in great shape as we tore the bike apart was impressive. Honda uses the right sized bolts in high-traffic areas, and it shows after a year of excessive abuse that a test bike takes. Through pipe comparisons, swapping plastic quite a bit, the random tear-apart for tech stories and the general neglect an "it's-not-my-bike" bike takes, we saw what stood up to the test of time at an accelerated rate. Little things like the airbox seams staying tight, and the shifter and brake pedals not getting loose or sloppy speak to strong durability. The bearings in the shock linkage and swingarm pivot seem to keep water and debris out and grease in as well. We had a couple of air filters we were swapping between, but the stock Honda filter is one of the most durable. Internally the engine still looked like it was brand-new and ready for another 150 hours, kind of a shame the bike was headed to the crusher (don't ask, it has to do with import issues). In reality, we lost track of the modifications cost on this bike since we were swapping so many parts and the regular maintenance was being done at the same time by a number of riders, so that figure went out the window, too. But if we had to compare the cost of keeping a Honda running, we'd say it is among the lowest out there as overall quality and durability are very high. Often I'm the first guy to say I'd wait a year on an all-new bike in case something goes wrong with the unproven design. I'm reluctant to risk potential big issues to get the benefits of the newer, superior performance. Well, it seems most of our Long Haul bikes lately have been the newest machines and, like this Honda, they have been proving my above concerns wrong. That is a really good thing. Now I need to go ride the 2010 YZ450F more!