The Barclay products including the fixer are all sealed in opaque plastic bottles so that there is zero air in them, I can't even slosh them around. I'd have to open to check!
I am looking at a Paterson PCS 1000 enlarger simply because the seller is willing to post it. I can't find much info on it although if it has a Paterson lens it may not be as great as the lenses you have mentioned. I have read of those lenses you recommend and you're not being too technical for me at all :-)
Can you recommend a crash course guide to enlargers?