So I sent copies of the images and a description of the problem to the original supplier to ask if they could advise a way forward or a telescope mount maintenance provider in the south of England. They forwarded my email to Celestron UK. They forwarded my email to Celestron US. I'm still waiting for a response! After much searching and watching videos, I decided to clean and regrease the worm drives.
On the advice of the supplier I ordered some Geoptik Equatorial Mount Grease, it comes with a pot for the worm gears and a less viscous pot for the bearings and shafts. I thought I would sort out the worm gears first and see how that goes and leave the bearings for now since they're less susceptible to dust ingress and it's a much more invasive operation.
This is the Declination worm drive with the cover off: (click the image for a close up)
The first problem was the Declination belt was a lot looser than the Right Ascension belt, probably caused by the grub screws to the right of the belt, there's two of them, between the motor block and the worm drive block, they were half way out instead of tightened against the worm drive block. There's three Allen bolts that hold the motor block in place but they need the grub screws to be tight to maintain the correct adjustment.
Then the cog on the motor drive shaft was too close to the motor. As a result the belt was only half way on the cog, only held in place by the flange on the worm drive shaft cog. I took the belt off, moved the drive shaft cog away from the motor a couple of mm and put the belt back on. Then I checked the belt tensions compared to each other, in both directions, with my eyes closed, using the force!
Once I was happy that everything was as it should be, I loosened the clutches and set the mount motors turning towards the home position. whilst they were spinning I used a tooth brush and a cloth to remove as much of the old grease as I could and reapplied the new grease. Again, I could have dismantled more and been more through but I wanted to keep things as least intrusive as possible at this stage.
So, I waited for darkness to fall then fired up
Target plotted dots in a straight line slope. After watching for a while I stopped guiding and started a forced calibration. Then the clouds came over and all the guide stars disappeared!
The forecast is partially cloudy for tonight, so hopefully I can try a calibration and see if my fettling has been successful!
It was the most fun I've had in ages!
Graeme