lee, on these the oil tanks do not get pressurised. the pump does just that. pumps oil out of the tank and in fact puts the oil tank under a small amount of vacuum. that's why the tank is vented. 'cracking' the cap open does nothing for these. if the saw is leaving oil everywhere it's time to check the area where the oiler seals up against the line and line area. if these little saws have been used much and are full of saw dust, combined with the way the exhaust exits the rear of the muffler (badly), the case warps a bit. most times a new line/grommet will seal up, but there have been a few on my bench I've had to use sealant to stop the oil flow. quite honestly, the oilers are extremely reliable on these. much more so then the little stihl cheapies. they don't block, they'll pump rocks if you let them
not plug at the sight of something slightly thicker than water...
when changing the crank seals on these, you need to be careful that you get the little wire 'gear' pretty much exactly right. it's easy to have the gaps uneven, too closed or too open. this will be the only time you'll have issues if you don't get that right.