Rubinar 500/5.6 - lubrication and other stuff.

I recently came into possession of a Rubinar 500mm/5.6 reflex lens. Real
cheap, like new. Came with M42/Nikon adapter.

I need an extension tube and/or a teleconverter to enable me to connect this
to my Nikon. No problem there, I have the right stuff on order.

Once I have the extension tube, I will need to recalibrate the focus, no
problem there, its a 2 minute job.

While I have the lens partly disassembled , I am thinking I should go a bit
further and change the lubricant for the focus, its really stiff.
I need a suggestion for a commonly available lubricant, one which will work
well in sub zero temperatures.

I also find the insert for the tripod mount to be a bit loose, I am thinking
I can use some epoxy to secure it. Otherwise I do not think I would like to
trust my camera to the mount. A sky hook would be nice but I cannot afford
one.

The price was right, but I wonder if it was much of a bargain. Time will
tell.

Any thoughts?

r.