Just a short observation regarding rear leaf springs squeaking:
Despite periodical greasing with chain-spray the squeaking persisted. I tried 3 different brands, jacked-up the rear, removed front covers of the leaf mountings to grease the rubber mountings with glycerine, etc. etc., no success.
Newly, in my desperation I used a rest of WD-40 - and see here, the squeaking disappeared.
This is not to promote WD-40, any similar product will do! Obviously, in some cases (like mine) the chain-spray does not have the necessary penetration power and something more viscous is required.
However, WD-40 does not grease, it just dilutes the solidified chain grease and helps further penetration. Maybe a hot air blower could also help, I still have to give it a try.
I applied now FluidFilm (as a spray) which has excellent penetration abilities and also water resistance.
Just as an idea for those who fight the rear axle squeaking.
Peter