Amsoil is good stuff, but 25K? for service interval? I would never let that happen. Two things about long oil change intervals.
One, the same acids, sludges and hydrocarbon crap forms in a top synthetic as forms in a dollar store ultra cheap oil and in the same amount of time. This depends on the condition age/miles of the motor.
Conclusion, the same stuff that creates the need for changing oil every 3k is the same with any oil.
Two, if you are the guy who buys the very best oil money can buy for your "baby", the last thing you should do is find out the hard way that saving $20-40 a year in oil changes just cost you a engine rebuild.
Newer manual transmissions seem to like thinner/lighter weight oils than the oe recomendations. AX15 during the summer will shift fine on the 80-90 gear oil that the service manual recomends, try shifting thru that pancake syrup in 0 degree temps. I use either durablend gear oil or in cases where they are already hard to shift and the tranny is not long for the world, 10-30 motor oil works great.
SD
amsoil guarentee's their oil, if anything on your motor breaks and it can be proven that it was because of their oil, they fix it for free, but guess what, no one has complained, do u think they would guarente their oil for that long if it wasnt good enough to last that long? my brothers 87 grand national has had amsoil in it since the day my uncle brought it home from the dealership, the oil has been changed once a year, this past summer my brother pulled the vavle covers off to change the valve springs and it looked like a brand new motor, there was absolutly no sludge at all
