My previous car was a 98 Corrolla, when I traded it in couple of years ago it had about 175K on it and ran like a swiss watch. Never consumed or leaked any oil. I had bought it brand new and did almost all routine maintenance on it, including vast majority of oil changes myself. The only reason I got rid of it when I bought my truck was it reminded my of my Ex-wife!
But what I did was when it got to high miles, if I remember correctly, around 80K or so, I started using Castrol high mileage 10W-30. The high mileage oils have special additives which soften and condition the seals and gaskets to keep them from drying out, cracking and susequently leaking.
It might be already too late in your case, but once you clean out the engine from sludge or gunk, etc. I would start using oils for high mileage cars to keep the seals from leaking.