[morzh]

A 16 is quite a bit of work, especially if it has been hacked, as you said it is, but then this is not the most inconvenient of the chassis to work on.

In my experience the black grime is tackled well by things as simple as Windex. if you want it sparkling (I never do that) then sure, strip it etc and clean, but .... why remove good 80-y.o. patina? Looks unnatural, probably never was that shiny when left the assembly line. To me clean enough is good enough.
US cleaning backelites is a bit excessive most of us spent no more than 10 minutes per cap and in most cases it remains clean as with gentle heating the tar falls out with very little left behind, except with those used after 1937 when they started flooding the eyelets, but then if you have desire and the patience....sure.

Pay attention to the power cord connection - 16 uses a shielded cord of some sort as the volume circuit is sensitive and will pick up noise.
Also see if the volume circuit has been hacked - there were several mods to it, with increased pot value, serial cap and bypass resistor. If your pot is bad - Mark Oppat has the replacements.