ML, 1000 and 3125 are intended for the same use but they're a different composition.
Looking at the data sheets, ML and 3125 are more oil based whereas 1000 is more synthetic based (polyethylene).
Main differences in performance seems to be how far each one penetrates and how long each lasts when subjected to salt spray. ML and 3125 penetrates further, 1000 lasts longer under salt spray.
ML is like 3125 but not as hard. 3125 can be used for underbody, ML is only really suitable for cavities.

I've not used 1000 myself.
Think ML3125 is a blend of ML and 3125? And I think that's the one I use?
