[Stig Jarlevik]

Hi

While there indeed was a Ju 52/3m with the WNr 5382 I doubt very much that
an oil sight glass
would specifically be adapted for a specific aircraft.
Surely an oil sight glass must have been mass produced and made to fit any aircraft on the market,
or at least many different aircraft types.

And yes an aircraft's WNr is the specific manufacturer's identifier of a single aircraft built.
See also manufacturer's serial number (msn) or construction number (c/n)

Cheers
Stig