something else to keep in mind with these C224 - C368 fusing units is that the black non stick film on the fusing entrance plate likes to crack and peal in the centre and cause fusing entrance jams.

You do not have to replace the fusing unit.

I disassemble it, remove the plate and slice off the offending section.

On one machine in the middle of the covid crisis where no fusers were available and i screwed it up - I removed the entire film and cleaned all the glue off. It's still working fine 3 months later.

Always seems to happen at the 300k mark on low volume machines (the factory fitted fuser, 4, 4e and 8 series have seen it)