Had cooling problems, then went into the office first time for a new gig, fan now producing loud howl/whine.
New fan ordered, made the replacement this morning, back to blissful silence and idling at 45C rather than 51C+.
It looked to me like thermal paste had rather spread out and off the CPU, but it’s 2.5 years, so fair enough. The fan also then finally was on the way out and maybe wasn’t doing so well, either.
Very, very glad I bought a FW.