Is this on your 1998 Corolla you posted before in the past? That had some oil consumption issues - something on the order of 1 quart every 5K miles? Seems to have gotten a little worse.
Head gasket replaced? Did you mean to say the "valve cover" gasket (or did you really mean "head gasket"? I believe that was mentioned in an older post, can't remember off the top of my head. If it was the head gasket - why was it replaced, overheated? That would be a completely different situation entirely.
If it was the valvecover gasket - possible the valvecover bolts has lossened up. I usually like to double check those bolts atleast once a year - make sure they didn't loosen up. More so immediately after replacing the valvecover gasket and then about 500-1000 miles later, to make sure there is a good seal. Guard against overtightening them - as the gasket is the o-ring type - seals best when the o-ring is not completely deformed (ie, squashed flat).
If this is happening more often - after installing a fresh set of plugs - check them after a couple of hundred miles, see if there is any oil on them. Take note of what cylinder they came out of. Clean the off, or install another set - check again. See if there is a pattern. If there are specific cylinders that are consistently wetting the plugs - I'd do a compression test (both dry and wet, to see if the measurements change - also do a leak down test to check the valve seals). See if there are cylinders that are out of spec.