I'm no valve expert by miles and miles, owned FT 101Es and have used plenty of other hybrid HF sets in my time. but take this with a pinch of salt ..
first place i would look Adrian is the drive.
the 12by7a driver valve can cause similar symptoms -
does it glow blue on TX ? mine does in my 101zd, (but its fine)
but it usually denotes a soft valve. not sure in the 101E though. all HF rigs i've owned, and the general rule is the PA will generally give a bit less out l as you approach the 10m band.
possibly the set was on 11m SSB and there was some tweaking been done.
depending on ability, u wanna get someone well versed in hybrid HF radios to check em. nasty voltages in there !
there's gonna be more folks offering better info Adrian, but i was just passing mate
this chap has something similar to read Adrian perhaps.