Sounds like the idler bearing froze on your LS. Both the idler bearing and the tensioner bearing should be replaced when doing the timing belt/water pump job in my opinion. The first thing I do when getting a new V6 (any year) montero is tear apart the front of the engine and replace the timing belt,tensioner,bearings and front main seal. Inspect the cam seals for leaks and replace if necessary. Ive used aftermarket bearings and T-belts with success but
would recommend you stick with the OEM front seal. As long as you maintain the timming belt and its components the engine should be fine..I have 185K on my 95 SR engine with just 2 t-belt changes and one tune up (I'm due) with no problems. Oh and ensure that whoever does your T-belt gets the proper torque on the crankshaft bolt..be sure to specificly tell him this even if it annoys him.