Hey guys,

My apologies if any of the following is blatantly incorrect or if I made a fool of myself by using the wrong terminology, I literally never had been under the hood before buying this car and I'm learning on my own with Youtube University.

1998 buick lesabre bought used at 157k miles and was told it was "in great condition mechanically". Engine light comes on immediately signalling P0171 and P0300, caused by running lean in bank 1.

Car is asymptomatic, idles very smooth and never looses power, even in the cold of winter. I took out the MAF and carefully cleaned it, popped it back in and wiped codes, as well as changed oil and topped off coolant. P0171 returned in two days by itself minus P0300.

While hood is popped and car idles, loud hissing can be heard, further confirming my fears of a vacuum leak. If car is turned off, the engine dies immediately, while the hissing takes a couple of seconds to die down.

The block where the air intake manifold meets the engine itself (right after the MAF sensor) looks to have an edge that has a gap, as if it was warped somehow. Hissing is localized to this area.

I bought break cleaner and sprayed it around the engine. Sprayed it right on that gap during idle, and car idle ticks up predictably. Bingo, vaccum leak located??

But now my question is, how should I proceed? If it really is this warped gap between the manifold and the engine block itself, can I just use some kind of heat-resistant caulk and caulk it up? Do I need to take apart the manifold further? I'm afraid to say I'm really not that competent yet, and I use this car as my daily commuter so I can't accidentally fuck the engine and have it unusable :(

Should I have a go at this myself, or try to get the dealership that sold me this to work on it themselves? They have a shop attached and I might get them to do some free work on it, but I'd rather do the work myself/shadow someone and learn.

What do you guys think?

EDIT: here's a picture of the exact area where hissing noise originates from and from where spraying break cleaner affects the idle:

https://i.imgur.com/IgWLbk4.png