Difference between TSK SX-M and SX-MHP?

[Chapparal350]

I need to replace a saltwater corroded TSK-SX-MHP (full assembly) and can't find one anywhere. I did find a couple of freshwater used SX-M units and I'm not sure if that would work for me.

Does anyone here know what is different with the SX-M and SX-MHP -- and if the SX-M would work as a viable replacement unit?

Thanks!