How to fix head gusket without taking apart engine

Do you have any yellowish cream under the oil filling cap? Change any freeze plugs? Water on the ground? If no water on the ground, check oil

Ignitiontune.....new distributrcap or plugwires..maybecoil or modulre

youve over heated the engine -and may have cracked the head or warped it -suggest you take to a ford mechanic a.s.a.p -an oil change wont solve the problem ,a new replacement head and new gasket etc.at the worst or may get away with just maching the head if its not cracked then with new gasket you could be lucky -talk to mechanic

this requires a detailed explanation and would be better served with a workshop manual as a picture is worth more words than this site can cover.

Are you talking about compression readings? If so, and you only have 30 psi, engine is in serious state of disrepair. The cylinder head will have to be taken off to fix the problem-sounds like a stuck valve, a non sealing valve, or a blown head gasket. There's no way to get to it without removing the head.
Apparently you had a compression test done? If you had done or would do a leak down test of that cylinder, it would pinpoint the source of the problem-whether an intake or exhaust valve, or a head gasket, or piston or ring damage. With a leak down test, wherever the air is escaping from the cylinder points to the source: if for instance, air leaks out the exhaust pipe, you know it is the exhaust valve not sealing in that cylinder. If air leaks out the intake-it's the intake valve.
Air hissing from the oil dipstick tube would mean compression is being lost past the piston rings-going into the crankcase.

No you dont need to reset anything,you replaced the headgasket,what is the warning light that you are getting.

Which engine? An overhead cam you take off without removing the head a internal center cam you have to remove the rockers push rods and lifters. then you can carefully pull it out.

Blown head gaskets for sure, no way of knowing if heads are cracked without taking it apart, there no quick fix for this, only fix is to take it apart and repair as needed.

Yes, this is very common problem of the northstar platform. Head bolts aluminum thread inside the engine block stretching. Although Cadillac improved it in 2000 year model, it persisted on a lot of cars. You will not see any water in oil, at least for the first 5-6 thousand miles, but it will get worse and worse every time, so aventually you will. Engine will "drink" your coolant and no kind of coolant additives will fix that. Especially big coolant loss will be if you floor your gas a lot. On the freeway however you can go for an about 100 miles before engine will consume most of the coolant and overheats. You need to fix the block, cadillac calls the proces "time sert" - they drill bigger holes in the block, thread it and put inside inserts with outer and inner threads, were your original head bolts will go. Dealer going to charge you $5500 for that, and most mecanics will charge around $3200. That is why so many people selling their caddys cheap on ebay saying that there is a coolant leak somewere. I bought two caddys like that. Now I can fix that kind of problem easy. I bought all of those expensive tools for time serting. And by the way, something I learn the hard way, even if you are mecanic but never ever rebuilded northstar before expect lots of problems and difficulties. Very complicated hi tech engine with balanser shauft. Parts are expensive too, upper set of guskets will cost you about $320 and if you buy all the lower seals too than $500. Piston rings $220 and good luck finding it in autozone. I guess it is time for you to find out how are those used car dealer shues fit you :-)

This is not a good question to ask.....I take it that you must not be too mechanically inclined...no offense. is this a v6? A head gasket is between the head(s) and the block. If a head gasket is bad (blown), then it is a very major job to replace. And hoping that your head is not cracked, which is sometimes possible. It is like tearing the engine apart, except for the crank and pistons (bottom engine) head gasket is on the top half of the engine. I would estimate that this job would cost you over $1000. without cost of parts. ???