So being basically illiterate about cars except for keeping up fluids, tire pressure and being sensitive to weird noises or behaviors, I would like someone to explain what the exhaust manifold gaskets do, and how critical they are to the life of my car. I had noticed a "tapping" noise from my engine and not being satisfied with my still learning about Volvos Russian mechanic ("need valve job"), I went to my old trusted Volvo mechanic 150 miles away. His diagnosis is the replacement of those gaskets. Seems pretty major, with a major price tag too but I do trust his expertise. I'd just like a basic explanation for my own edification as I nurse this baby over 250k miles. And what else should I be asking my mechanic to check while he performs this bear of a job? Turbo air and oil cooler hoses? O2 sensor? (These questions came up as I perused your repair information) Thank you experts!

It really shouldn't be that bad of a job if he's putting heat on those nuts so that they don't snap the studs in the block. If the turbo has a manifold to downpipe gasket, you should change that too.

When I did my 1989 740 turbo exhaust, I dermel tooled all the Ex. manifold nuts off on the flat edge of the nut down to the threads. I then use PB Blaster onto the cut edge so the solvent seeps into the threads. make sure all the special washers and spaces go back properly so the new nuts hold down the ex. manifold. If you fail to replace the hardware correctly, the manifold will loosen and blow out the gasket.

I have had a problem w the #4 cyl on my 93/940 ,,,2 nuts just seemed to have dropped off somehow,,Im searching for a donor engine or car so that I can get the head cleaned up machined if needed & all bolts drilled out & replaced.
That way Id be able to more easily swap heads,,,luckily mine isnt a turbo,,I once got an 87turbo for free & it was the biggest waste of parts & money,,Never could get it to run right