HS-81s are good servos, but due to their "mini" size, cannot withstand abuse or shock like a standard size servo. They should be fine on the ailerons, but I would install the metal gear kits in them if you decide to rebuild. The ARF version of this plane has individual aileron servos. Mine has HS-5485HBs all around.
http://www3.towerhobbies.com/cgi-bin...?&I=LXUW28&P=Z
or for $2 more, upgrade to the HS-82MG.
http://www3.towerhobbies.com/cgi-bin...&I=LXTRE2&P=ML
Looking at your posts, it seems you were running a 14x7 3 blade?
http://www.rcuniverse.com/forum/ques...l#post12080807
From experience, I have never had good luck with 3-blades on 2 stroke engines and the one you chose, IMO, was far too large for the AX75. I tried them a couple times and never went back due to poor thrust and speed.
For your current 91, I would recommend you use a 2-blade prop called out in the manual. Once you learn the airplane and are comfortable with it, you can always test different propellors to see what they'll do for you. Don't overthink it, just use what OS recommends and get 'er back in the air!