Hi,
I had similar with my predators and was going to chuck them so as a last resort I tried the following :
• Ran the hottest sink of water I could, added a large dose of dish soap.
• Let them soak for 10 mins or so.
• Used neat dish soap on a natural (soft) bristled brush - really agitated / scrubbed it well around the lens.
• Repeated the soak and scrub a few times and then rinsed.
It worked really well ! They have probably been through that cycle three times now (due again soon …).
They don’t seem to have suffered in anyway from this type of cleaning.
Worth a try - what’s the worst that could happen ?
WD 