I rang Bintel today for advice and the tech there told me that with my scope being around 10 yrs old it should have a serial number etched into the glass near the edge. The line should point to that. If not it's a Chinese model and I'm stuck with trial and error.
At first I couldn't see any serial number at all.
But after searching with a magnifying glass I found it under a black mark I made marking the shim positions.
The line now points to 3 o'clock with the label just off horizontal.
When the weather clears I'll give it a star test and let you know how it went.
Thanx again for your help