So, back to the OP. Seems it was you. Loosening mount bolts means either no maintenance (checking the bolts, especially after the first few runs) or poor installation. The plastic backplates do loosen due to thermal cycling, but again, it comes down to maintenance, nothing to do with the engine/quality. The other engine killer is expecting too much from it, especially simple plain bearing engines like the LA's. Screwing the neck of it with too big a load and needle tweaking will destroy them pretty quickly. Look after them and they, and all engines, will last well beyond what would be considered 'normal'. For another instance, the LA 46 in one of my aerbatic models has just had a liner/piston change, but first flew in 1998...just another example of poor quality OS liner plating? I have no idea how many hours of operation that represents, but given the size of the engine, and the number of miles that piston has travelled up and down that cylinder, I ain't complaining...
Evan, WB #12.