I've been pretty blessed with respect to drive train maintenance. Only once have I had to replace a set of sprockets and a chain. And, I really did that because I was taking a long trip (Trans-Am Trail - Oklahoma, New Mexico and Colorado) and didn't want to have to worry about the chain failing. The original equipment chain probably would have made it but I figured "better safe than sorry."
One the things the previous owner did, to ensure the chain wouldn't turn to junk, was to liberally apply (red) grease to the chain. He did a nice enough job because the chain is still in pristine condition but the grease attracted an awful lot of dirt and debris along the way. Over the winter I made a feeble attempt at cleaning it using rags and brake cleaner. That was good enough for the time being but last weekend, while I was changing tires, I decided to get it good and clean once and for all. This time I used about a pint of turpentine, in a shallow oil drain pan, and let the chain soak in it while I swapped tires. Using a little elbow grease and an old toothbrush did the trick. The chain now looks like it did when it left the factory. I opted to try some Liquid Wrench Chain Lube.So far it's been great. It goes on as a liquid and dries within sixty minutes. It does not sling off but you do need to be vigilant while applying the lube to the chain, as it will drip. The next time I apply it, I may remove the chain from the NX and suspend it so extra liquid lube can drip off into a catch pan. After its dry, putting the chain back on the bike should be easy and keep everything much cleaner.
I am kicking around the idea of changing the sprockets so I can get a little more top end speed. Stock gearing for the 1988 NX125 is 15/56 (3.73:1 final drive). The 1989-90 models came with 15/50 (3.33:1 final drive) gearing. I am thinking of switching to 14/48 (3.42:1 final drive) and an o-ring chain. I will stick with the 428 chain as I see no reason for an upgrade.
EDIT: a reader left a comment (thanks Ed) to let me know that the stock gearing, on his 1989 NX125, is 15/48. So, if I wanted to increase the top speed potential, I could always go with the factory gearing for the 1989-90 NX125.