I was reading a post a week or so ago and someone mentioned that 21-2388 series combines usually need a rebuilding after i think it said 2000-2500 hours? If this is the case, wondering what they mean? My 2188 has 3600 engine, well i guess actually 50 hrs on an overhaul, and 2800 separator. Starting to see a few cracks, etc. like end of cross-augers in bottom of hopper. Is there other things i should look for? Already have new AFX rotor, concaves, sieve rails look ok. Thanks for any input.