I think that is correct. The sleeve and piston mate for life. I have never tried to resleeve one I just use that as an excuse for buying an upgraded motor. Do you have a temp gun? They cost about 30 bucks and give you a concrete answer to the question is this too lean. One temp gauge can save countless motors and pay for it self in saved money and time. Once I got one I felt much better about my tuning.
you can send the motors back to traxxas for an exchange for like 110 bucks or get a used one with pleanty of life off ebay. I just for a 2.5 for $54 the other day. It arrived in a short time and has lots of pinch (compression).