the 70s have plasticoat
or plasti kote
the original walb' product was intended for THAT coating...
see post #13 and #27 and beyond in this thread...
looks like 'superseal
' is the first choice, with cleaner, polish n glaze
for naked skin streams...
because the older plasticoat
was soft and HIGHER in plasticizers...
a modern 'vinyl spray' might also be useful, at least it will be SAFE on the old coating.
vinylex made by the lexol folks is a good example, but ANY of the older style vinyl sprays may work.
the "hand prints" seen may actually be residual SOLVENTS or grease/oil stains...
IF they've soaked INTO the old finish it's possible they will be visible till it peels...