im at almost 10,000 on my T444E and it still runs like a Champ.. ive got it tuned and am getting ready to put injecotrs in it but have no reason to believe it needs rebuilt yet.. a lot is how an engine is cared for.. ive seen some with 15,000 hours srtill running beautiful and ive seen some at 7000 hours with so much blow-by it was fogging for mosquitos out the draft tube.. you just have to check it out.. listen to it.. look at the blowby.. drive it.. does it skip? does it run smooth? etc