Ive got one I bought from Oreillys about 3 years ago.No trouble so far.I do believe thats all they replace is only the bad components. Most likely the caps,signal return trace repair and an occasional power transistor.These are the main problems Ive seen occur,but you do bring up a valid point about the remaining components being the original....
You could always attempt to replace the caps yourself before either sending yours out for repair or buying one already repaired.The caps are only a few bucks.If the signal return trace is damaged,you can verify that by running codes and having them present for the evp,bp,ect,act & tps.If codes for these sensors are present,the signal return is open on the board and it can be repaired by soldering a piece of 32ga wire across the damaged trace.If a transistor is bad,it either triggers the cel to stay lit solid when running codes or codes wont be flashed at all,regardless of which connection method you use with the jumper wire.A member on another site had his caps replaced for a continuous fuel pump running condition,but other issues were apparently present because the ecu still didnt function correctly after the repair.Maybe the repair guy put the caps in with the polarity reversed,who knows.Regardless of whether you buy a reman unit or send yours out for repair,the same things are gonna be done.Caps,trace and transistor.If something is damaged beyond that,they'll likely just send yours back to you and state it cant be repaired.
91 LX 342ci (10.5:1)
TFS 190cc (stage ll)
GT40 (tubular) intake
Weld ProStar XP's