I'm not sure what you mean by the "liquid screen protector stuff".
I put an IQ LiquiShield screen protector on my 2XL. To install you sprayed the supplied liquid onto the phone's screen and the back of the screen protector then laid the protector down, positioned it until it was aligned and then used a soft rubber squeegy wedge device to flatten any bubbles and make the protector adhere to the screen.
One thing I liked about it was it could "self heal" with the use of a blow-dry gun. I got superficial scratches in the plastic screen protector but if applying a slight amount of heat with a blow-dry gun would make the scratches would disappear.
I wish I had known about the vegetable oil trick. I did use a small drop of water underneath the corner that lifted up on my screen protector, then press the protector into place. Yes, it fixed it for about a week, then it would peel up again. I'd put another drop under there, press into place and it would stick for about another week. Used to drive me crazy.
I can see where vegetable oil might hold a peeling screen protector better than water, but I'd worry about it yellowing in that spot or peeling up again.