A leak at the exhaust manifold - at the head - draws minute amounts of cold air in on the cycle which can burn exhaust valves. Perhaps this isn't a problem w/ 240s but it's common on various cars that go through exhaust manifold gaskets eg. older < 1970s MB gas engines.

Your leak is further from the head so probably not a concern.

I'm fairly casual about fixing things on my 240s but this is one thing I fix ASAF.
--
240s: 2 drivers and some parts cars

Do your mechanic a favor and apply PB Blaster or other good penetrant to the header nuts and studs several times before the job . Your shop bill may be lower, too, in the event those fasteners prove stubborn.

Chris in VT, '94 945 w/ 171K

I'm with porkface...Drive..windows down,,ventilation on full.
My 85 240 had the same problem, and I finally replaced the gasket with one I bought from FCP Groton...It was a piece of crap and it blew out.(nothing against FCP, and it's possible my installation had issues and/or shortcomings)?...anyway, the long and the short of it is that I happenned to have an old Volvo OEM gasket that I had salvaged off a partscar, and there was a big difference in quality from the FCP aftermarket gasket.I have logged over 50K miles on the old used Volvo gasket..no problems.
Bottom line;there's no reason to not drive the car for a few weeks with the bad gasket...heck, I drove mine for several month with a bad gasket...it sounded kinda like a tractor.

best wishes

noise. don't worry, just drive it. good luck, chuck.