The original lifters are a known problem area due to their small oil holes. It wouldn't be a bad idea to replace them with the updated lifters while you're in there if they're making any noise right now.

The best price I've found them for is here: http://www.store.partsdinosaur.com/product224.html

95 Montero SR
3.8 MIVEC, Advance headers, 2 1/2" exhaust, Magnaflow muffler, OME shocks & rear springs, 2" body lift, 3" tank lift, 4.90s, TRE front locker, factory rear locker, Roger Brown Rock Sliderz, 315/75r16 (35") tires, Sport big brakes