I have two Facit C1-13 calculators. One is from the 1930s (green) and the other is from the 1980s (white). The later model has one of the highest documented serial numbers 2369426. I had to restore the older model because all of the lubricant had gone bad (oil to sludge), so I cleaned it and used synthetic oil. It was a full strip-down (everything taken apart) — about 20 hours of work over two days (probably not going to do that again). What's nice is that to get them working again all they need is a bit of cleaning and oiling, the mechanism is very durable (though I did have to JB-weld the 0-button back together).

Inside the younger model:

My second one from the ~1930s

My gloves mid-way through refurbishing the calculator