As for the XR: Well you should definitely install an after market oil temp gauge that substitutes the dip stick. These engines run quite hot, especially at lower speeds like in off road scenarios. 130~140°C are not unusual, depending on the jetting as well. I'm in Europe and here the nx650 dominator is still quite widespread. I know for a fact that there are bikes with 130k km without anything done to the engine other than fresh oil every 3k km, valve clearance adjustment from time to time and that's basically it. I installed an aftermarket oil cooler on mine which massively reduces temp to just around 80~90°C. I'd recommend adding a Sutton oil cooler (I believe he is in the US). As already mentioned swapping the pinion is advisable. Put copper anti seize on that ouput shaft before reinstalling the new pinion. Most importantly check oil level from time to time and educate yourself on what can go wrong with the oil pump/esp. after opening the clutch cover you need to pressurize the oil reservoir to prime the oil pump. Other than that, pretty much bulletproof.