[glend (Glen)]

I have priced the replacement focusers, the Starlight and Moonlight are both going to cost around $500 USD plus shipping . If i bought direct from Moonlight in the US I could get it delivered for $600 AUD. The Baader Steel Track and adaptor is a lower cost option at $450 AUD landed but it seems to be exactly like the GSO rail focuser that I have on the RC08.
I use the exact same GSO rail focuser technology (newt version) on my 10" imaging newt and have never had a problem with focuser flex/sag on that scope with my heavy cooled DSLR (and it's a non-rotating scope so sometimes the camera is hanging at very severe angles).
I am having a real problem justifying spending half again the cost of what the RC08 cost me to buy a replacement focuser. Altair Astro advise on their website re the RC08 that the standard GSO linear rail focuser:

... will handle a DSLR or CCD camera, and a light weight filter wheel perfectly well, and is adequate in most imaging situations. Note this focuser has the Linear Bearing upgrade, and will outperform most Taiwanese dual speed focusers, both in rigidity and pulling power. It is perfectly adequate for a DSLR/CCD camera and light weight filter wheel.

I will take what steps I can to improve the stock focuser first.
So I have stripped down the stock focuser and tightened up the rail bearing screws (which seemed fine anyway) and firmed up the pinion shaft that presses against the rail - its all now tighter than my 10" newt focuser. I can not force any sideplay in the focuser rail nor up/down sag/flex that I can detect.
Reading old threads about this subject suggests that the bevel and stop ring placement on the focuser flange mount might be a source of bad fitting so I checked that as well and made sure the stop ring was in the best position to be pushed against by the locking bezel. I can't really do more to QA the stock focuser.
A new round of star tests will now be done at various mount attitudes looking for indications of sag/flex.