Need help with my Telescope L1A1

[Surpmil]

Thanks everybody for the help.

I tried today with the telescope mounted into the bracket and to the rifle. Clamped the rifle into a vice and leveled it horizontaly. The crosswire levels exactly horizontal and the post runs up and down exact vertical. Used a string and plumb weight to control.
But the top of the range drum is not parallel to the crosswire. The deflection drum is square to the leveled rifle.

Even with the top surface where the range drum sits on is not parallel it works correct and thats the most important thing.

I have another question about my L42A1. The rifle came with a wrong rear sight. There was a No8 rear sight with battle sight removed on it.
I am now looking for the correct sight Mk1 converted to meters and marked with M.
Knowing that they are very rare, is there any chance for getting hold of one???

Sounds to me like someone has cross-threaded the knurled portion of the drum onto the "core" or "shank" - whatever one wants to call it. Is there a fine grub screw present where the two join?

[Mk VII]

I've got some of those modified slides here somewhere, if you need one.