The caps with the flip-up lids are actually oil reservoirs. Often they have a lamp wick in them, which soaks up the oil from the reservoir and allows it to ooze into an output channel by capilliary action. I have a bunch of them on my ancient power hacksaw, at least one missing its lid, and most of them with no wick so they are just reservoirs with no slow-feed function. Good luck getting a lid for yours - but you might get some complete oilers from a junk stall in a flea-market, or on ebay. If you find a bulk supply of them, please post about it - I can't be the only one interested.
If you have any with screw-down tops, they are grease lubricators. Each time you give the top a half-turn tighter, it forces some grease into whatever is being lubricated. They work very well, but are messy to refill.
