I was going to use some lighter fluid to remove some of sticker residue from an old ps1 factory sealed game, but I'm afraid of the plastic being so old now, will the fluid seep through (because plastic breaks down over time becoming more porous in theory) anyone have experience in this? Thanks

I would refrain from doing so. Don't quote me, but I believe WATA has experience doing this. If you send it in for grading and select the one of the cleaning options it's included. You can call them to verify it. 
I believe first they analyze it to see if it can be removed or not. 

Go hard. Obviously apply the fluid to a napkin or cloth first, and then apply to the cellophane. I have no idea how long plastic degradation to the level you're talking takes to happen, but factory sealed games are not close.

From the grades I've seen, I doubt Wata even penalized for stickers. VGA seems to be way more strict.

I've done it lots on sealed NES games, don't worry about it. Put the lighter fluid on a Q-Tip and then apply it to just the sticker. Getting a little on the cellophane won't do any damage.

Haha I like that, go hard... But use a qtip....

I actually did it to my Castlevania game personally for me just because the white ass sticker stuck out the black cover. Overall good results I think. Thanks for the input all I'll put some follow up picks