Ya, SRC T91 I believe is the worst out of the available T91s T.T (WE T91 externals are WAY better, but then it is also like 2 years newer lol)
However, the good news is the body is not pot metal
, main complaints I personally have with it, is perhaps outer barrel colour, orange flashhider, upper handguard is too blocky imo, front sling has no spring to keep it from moving around freely, and the buffer tube...
For replacement parts though, from what I can see, it should be completely version 2/m4 compatible, and I'm guessing the only hard replacement to find would be the front sight I guess, although that can easily be custom ordered by an SRC retailer I guess.
Now I just need to find a way to get my hands on a LY T91