[R-390] Y2K Manual Question

[Don Reaves]

In the y2k manual, there is mention of two lubricants for the gear train
and slug racks.
One is MIL-G-7421, which is a grease and is easily identified on the net.
But the other is MIL-L-7970, which is likely a typo and should be numerals
7870.  MIL-L-7970 is a specification for mahogany plywood, whereas
MIL-L-7870 is a general purpose, stable at low temp., instrument oil with
anti-oxidation properties.  That part number is superseded by part number
MIL-PRF-7870.  7870[D] seems to be the last available revision and Royco
lists that oil as commercial part 363.  Anyone disagree with my conclusion
that 7870 is the proper citation?

The reason I ask is I am engaged in a discussion with a friend about the
merits of not applying any lubrication to the R-390A gear train after
cleaning up a dirty mechanism.  He likes dry, I like a little Mobile-1.  I
was reading through the TMs on the subject and discovered the mention of
these two specific lubricants and wondered what they were.

Don