The oiler buttons on my import 16x40 (which I am generally satisfied with) are utterly useless. I have never been able to successfully inject oil through most of them (only two work, actually). This includes fiddly tweaking with Luer tip needles on manual squeeze bottles to shove oil between the depressed ball and the rim of the button, and using a high-pressure oil gun with a cross-slit tip to depress the ball while leaving a free space to pump. I've even tried pooling oil on top and then jacking the ball up and down with the tip of a scriber. As far as I can tell, these damned things are installed in blind holes! If there is any "window" of open oil passage between ball-up-and-full-closed and ball-down-and-full-blocked, I haven't found it in more than 5 years of playing with it.
I have not yet succumbed to the temptation of ripping them out with a woodscrew and a pair of needle-nose pliers, but I am getting very, very close. There are only a couple of oilers where a small filler cup would interfere with something (like slides passing overhead) and I'd be happy enough to plug those with felt or something.
In the meantime, the maintenance routine is very old-school. Dribble oil on the slides and run things back and forth weekly (daily if using heavily). Every six months (nine to 12 months if day job keeps me out of my own shop) take the compound and cross-slide apart, manually clean and lubricate.