I'm currently a bit over 100K on the original engine. It's used oil since about 40K miles perhaps....recently I switched to 15w-50 Mobil1 synth instead of the 10W30 synthetic. I've used synth since day one, either Royal Purple when I'm feeling frisky to off the shelf Mobil 1 synth(which if you didn't know, is no longer a true synthetic but a highly refined dino-based oil like Syntec). Oil consumption problems stopped with the switch to the heavier weight. Being in subtropical Florida, the heavier weight isn't an issue. I JUST replaced the sparkplugs for the first time...they were almost gone, worn down to the electrode "nub". Replaced them with stock plugs. I use Royal Purple in in the tranny, transfer and diffs. It's never been in for regular maintenance (other than oil, tranny and bearing repack for the hubs) and is still going strong. If we don't trade her in for a "vert", I'll probably spend the money to change the belt and have the valves clearanced.