The 4x was still perfectly good, the 100x unfortunately had dirty lenses. Probably old immersion oil plus some growth (?), not sure if or how this could be cleaned. Regardless of quality, it just didn't look right. Similar to a twenties typewriter with plastic spools - perfectly functional but not 'right'.
Fortunately in the online era, it becomes possible to scout and buy parts globally. These objectives of the 'double knurl' type are not all that common and just don't happen at all in Europe. So at (surprisingly considerable shipping) expense, found and got shipped across the Atlantic replacement objectives of the correct type.
This looks much better (to me at least ;-)
Very lucky that also the new 97x high power objective seems to be in excellent order. Clean and gives good image. From the serial number MK7316 this particular objective was manufactured in 1943. Probably won't be using the oil-immersion objective all that much, but good to have the complete, functional set.