We've been here before!
Deoxit is expensive but the BVWS sell it to members at a keener price.
I've always been happy with Servisol Super 10.
WD40?
It's fine for many little lubricating jobs around the house and car, but I can't really think of anything I'd use it for on a radio.
My eyes glaze over when I see posts saying "how can I get this grub screw loose - I've soaked it in WD40 for days". Why am I not surprised? As has been said, WD40 was primarily intended as a water displacement fluid - not a penetrating oil, although the makers do claim that 'it loosens rusted parts'. It penetrates to the extent that it's thinner than lubrication oil such as 3-in-1, but really, something such as Plus Gas Formula A dismantling agent is a much better bet as it has a very low surface tension.
You probably won't find it at Halfords, which markets its own brand of a product it calls 'Shock and Unlock Cold Spray' in 400ml aerosols, which it claims 'combines 'powerfull' (sic - Halford's spelling error - not mine!) penetrating fluids and freezing agents which "shock free" rusted agents and jammed connections'.
Plus Gas Formula A here:
http://www.my-tool-shed.co.uk/m129/P...FaQA4wodvkBBvg
Shock and Unlock here:
http://www.halfords.com/webapp/wcs/s...egoryId_165594
David