Rbtdanforth - thanks for the input. Today I took a look at both the assist fan and the purge fan, made sure both were nice and clean and also gave the contacts a good clean with a wipe. Certainly seems to have spruced up the assist air, but alas still fails to cut through on older settings.
As well as the above, I also cleaned the lens/ both windows/mirror/focus sensor windows yet again, had a very close inspection of the lens (couldn’t see anything at all) and needed to cut out a piece of acrylic for a picture frame. I used a piece of proof grade and it didn’t cut through until I ran a second pass - I guess that largely rules out moisture content of the wood being a potential issue.
Something I forgot to mention but feel that I should - There is a very light scuff off-centre on the laser head window but there always has been, glowforge credited me some store credit for the damage for a replacement piece. Sadly as they (still!) do not yet ship internationally from the store, I have been unable to actually order one despite the credit.
That said, the scuff is very small and completely unchanged from when I received the unit. Very first ruler I cut out worked but proof grade has always been slightly dodgy in terms of reliably cutting out, usually requiring some clean up on the back. As you will see from the pics now, proof grade performance has become substantially worse in addition to speed continually having to be reduced for our normal materials. Given the scuff hasn’t changed at all in appearance, I find it unlikely to be the issue for a continual power drop off but as glowforge stores shipping policy remains US only it is currently difficult for me to acquire a replacement it’s hard to rule it out.
Printed the gift of good measure as requested on medium draft board. As always, crumb tray is sitting flat with no dirt in the alignment divots, the surface is clean and the wood held down extremely flat in this area by several strong neodymium magnets. Proofgrade settings were used (as of the time of this post it is the most recent print for glowforge tech support if you want to look at it, 30/08/18 at approximately 11:58 UTC ).