A friend is having problems replacing his 8 speed set up with some new SLX kit he's got (Specifically the rear derailure doesn't "fit")

Has anyone had any experience of newer kit not fiting onto an older frame

I think he's got an old Specialzed Hardrock. Not sure about the vintage, but possibly before 06 when the mech hanger changed to the one used on todays Rockhoppers/hardrocks)

Should be absolutely fine, you could fit it to a 1990 Hardrock if you wanted. He's doing something wrong.

I've got a 2002 NRS frame so pretty old and the shadow XT went on without any problems. Even on a 1996 Rockhopper my friend recently got newer Alivio went straight on.

Now depends how good Your friend is with bikes as recently my mate told me his friend had a problem with putting a new SLX on his bike, but it turned out he unscrew the black part that screws onto the hanger as he thought it is some sort of a mech hanger and he already has one on his frame… It may sound stupid but did You see how he was trying to mount the mech or did he just told You he's got a problem with installing it?

I had to speak to him on the phone and it turns out he had removed the mech-hanger and old derailure as a single unit, and couldn't understand why the new derailure wouldn't fit straight onto the frame!

I fitted an SLX rear mech to my '04 Enduro earlier this week and it was no problem.