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Any recommendation on type of oil? I've got tons of bike lube...Careful use of heat and cold usually works on seized alloy pneumatic speargun parts... pouring hot (not boiling) water over the affected area then running under cold tap. Spray some light silicon oil into the threaded area and it should wick in.
Repeat a couple of times.
The other thing is you need a 'soft' way of holding the filter firmly without distorting it... I use one of those silicon egg rings
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I just wet it - not soaked. Will soak though.Assuming salt water dives?
How long have you soaked it? I would start by giving it a day or 2 in a pail of fresh water.
Then try more brutal stuff starting with a few light taps.
No lube. Unless you are really sure you know how to clean it off the lense without scratching it...Any recommendation on type of oil? I've got tons of bike lube...