The manufacturer says you have to keep it between certain levels of relative humidity. Searching Mitutoyo documents I can't find the figure for their objectives but they quote upper levels of 70% or 80% pretty generally. Yours went higher!
If the vendor didn't ensure that would be maintained in shipping, then
he mishandled it.
But about 99% of of the objectives which come to me, are thus mishandled!
I'd test it, and may find it's fine, but would always have a concern about it which would be greater than for a camera lens.
If buying a used thing then we
never know the history, which is why we pay hopefully
much less than the new price.
My hit rate for "perfect" Mitutoyos, many of which have had to pass through CS's critical hands, is of the order of half. It's hard to tell because there's variation between the good ones.
I feel it's ok to accept something which works well enough, if the price paid is low enough.
If it's a $2500, 50x, objective and I paid $500 then the bar is lower than for a $800 10x for which I paid $500.
If your objective has a seal which is faulty, it may get worse, who knows.. I have objectives which don't work as well as I thought they did. Rik has a documented case of a 10x which "went bad" and he replaced. We sort-of assume it was knocked, but we don't know.
One objective (7.5x) went back because it looked fine but was way off what it should have been. It reappeared for sale as "tested", at the same price. Same vendor, with a different ebay account.
Sorry if this sounds like a lecture
, just how I've come to look at the murky world of ebay.