Unscrewing super-old lens cells

[Yourix]

I first tried the hammer technique but it did nothing and I was a bit worried to damage anything.
It finnaly came loose with some penetrating oil, patience and a pair of heavy-duty rubber gloves...

Thanks to everyone

[komatsu]

I've found you need to be patient with the penetrating oil (WD 40 in my case), when using Alex's method. Let it sit a a couple of days, then the hose clamp and hammer.