Protective coating for older/weathered paintwork...

[JonE]

I use the oils which harden and 'set' on rusted steel plinths after sanding them occasionally - so boiled linseed often. The difficulty is finding something that stays transparent rather than yellow tinted, if using on anything other than rust colour. You joked elsewhere about engine oil getting onto your clothes for oily rag, but I reckon there are advantages in the non-setting oils just for maintaining surface contact, done regularly enough and polished back enough?
What colour is the paint... ?