RE: AMT 280 SP
I have an AMT that is from 1994, and as far as I know, it's only been serviced once. The old AMT's are great engines, but when you do have a problem, they are expensive to fix. The other down sides are that they are much heavier than a modern engine, (you are looking at 2 Lbs more for the complete installation, on the AMT-180 over something like a K-80) and the air start system is bulky, and heavy, and you have to get a SCUBA bottle filled every once in a while.
As far as AMT not requiring you to send it in for service is true. They only give you a 2 year warranty on a new engine... and they will run WAY longer than that. AND... the V1 ECU's don't keep run time in them.
The only companies who actually require (or demand) a service are the ones giving a life time warranty. (kingTech and Jet Centeral) Wren is the same way. They don't want to see an engine unless there is an issue.