G'day. I too would like to thank Cheap6 and 88GreenVN for excellent postings. In our case the patient was a 1990 VN Commodore driver's seat.
We followed the instructions to the letter (unfortunately we found the centre cap on the recliner knob could not be taken out without gouging, and this was removed using an extremely thin-bladed knife), only to find at the end that the slipping was unchanged (a new circlip may have improved matters, but of course the dealer was closed on Sunday!).
In desperation I slipped a piece of 80-grit wet-and-dry sandpaper (cut-and-holed to match the mouse mat rubber) on first, rough side facing the reclining mechanism, then the rubber, then the retaining washer, then the circlip. Voila! No more slip. Cheers fellas.