Cleaning and lubing

i used to use a cheap cross-country chain oil from a bike shop, a thick green oil that seemed to just pull dirt to itself and gunk up the chain. gt85 every now and again seems ok, maybe something more heavy would be good but what?

any of those chain oils are fine.

You can use gt85/wd40 to clean off old gunky oil& grime.

Then apply your chain thicker chain oil liberally.

Then importantly, wipe off as MUCH of the oil as possible with a cloth.
You are aiming to leave only the inner concealed joints oily.

Some people actually use WD40 again at the end to take the excess oil off, but you have to spray it into a cloth and wipe off carefully otherwise youll strip the oil off again!