In talks with TOC, the way they used to operate was just to send a new loco, and scrap the unit you sent in.
When times got tight, the service has changed to the way you describe it Rky...
I wonder if they never developed the expertise to fix things properly in the first place.
The part that really gripes me is that people have sent in locos that were in a trim/roadname you could no longer get, and the would often get a loco back of similar but actually lesser value.
The worst happened when the loco is no longer manufactured and you get a completely different loco back.
Sorry this has happened to you, but unfortunately it's not surprising.