Tony,
I'll bet you have slight rust spot on rear inside of your hatch, driver side.
I do on mine and I have a true California car.
It's because of the lack of quality (yours like mine was original & aged) bead on the window to hatch.
Go visit any glass shop they have the right sealant goop. Sealant is dispensed in a caulking gun. It is black sealant in color. It was a no-name type (not 3M or GE).
The sealant this glass shop used was a type where there was body shop tape placed over fresh sealer bead, to help overnight curing. Next day I removed the body shop tape & had a perfect smooth surface on bead.
It's rained in SoCal several times since that fix.
Not a drip my trunk area bone dry.
SO COOL
Know how nice it is to be pamperped at a car wash? I can't wait to take my car thru a car wash & have someone else vacuum for me!
This is my FIRST LEAK FREE I OWN IT CAR!
Last time I sent a I own this car thru a car wash I had car wash break my rear mount antenna.
Opps! That was back in 1983 or 84 I believe. Haven't used a car wash again (I washed by hand), since then. But will now that my Firebird back window doesn't leak.

i'm not going to pay a glass shop to seal my window, i'll just buy the stuff, oh, unless thats what you ment?

if so, how do i get the old sealent off? do i jus put the new stuff on over it? will masking tape work?

P.S. thanks for all the non fuel related info, i love this board

For the money effort & proper job done, give the glass shop a couple bucks.
For my rear glass leak, I too, thought ya dig out channel etc.
Nah.
They just laid down a super thick bead (about 3/8") one stroke across trunk lid/glass area. Done in less than 30 seconds. Cover sealant with body shop tape, as your paint is good. Use the least left over tape residue stuff! This is same blue tape stuff as inside house painting tape. Easy to get & the glass shop will have it, too.
I've never seen the sealant brand or packaging before. It was a shiny silver tube with black lettering. Again, not 3M or GE brand.
I got my front windshield glass replaced by shopping around the local to me wrecking yards.
Outta 5-6 places, I was given $120 new to $70 used. Yeah I chose the used & no complaints either! I'm going back to same place & have my 1985 S-10 Blazer windshield replaced by them, too!
Go shop around.
I mean if ya charged over $5 by a Glass shop ya paid too much!
PS Tip, make sure ya get the goop into the corners, smooth & securely.

PSS I've tried sealing glass at home.
Over the years, learned a few times & blew many more sealing!