The difference is
DIY= strip it down,de- grease ,remove all manufactured burrs,if metal guide & top hat,replace with plastic/ Delrin guides & top hat,polish all internally but don’t be to particular with piston,if ribbed ??
this is to stop the grease/ paste, from migrating forward to the piston.
breech seal replacement/piston seal / bearings?
if competent enough
strip trigger de-grease, polish sears/ adjust pivot pins,( personal preference)
there is a little trick I perform with the TX trigger, which will remain mine/ fettle
reassembly .