Yes, Redcat does have a engine replacement program.
basically sending in the old motor will get you a replacement at 1/2 the retail cost of a new one.
details on this page:
http://www.redcatracing.com/information/warranty.html
as for the TRX .15, if there is room to move the motor mounts just by drilling new holes, that is what i would do. Easier IMO then buying a new clutch bell that will reach the spur gear.