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This Precisa mechanical calculator worked well on plug-in.  Even the noise suppression capacitors seem to be OK.

The motor with all electrical parts form a single unit attached on two steel rods and kept in place by E-clips. I guessed that 50 years old oil doesn’t lubricate very well anymore, so I took the motor off, partly disassembled it to get to both bearings and applied some fine oil.  I also oiled the main bearings in the machine and made sure that all parts were easily moving.

Ink ribbons are not widely available.  I found a Dutch supplier who delivers worldwide and has a very wide collection of ribbons and other calculator and typewriter related supplies.  See Links.