I'd like to clarify a thing or two...
First off, did the old manifold blow up or was it just leaking?
Second, if it didn't blow up, was the car running well before you removed the manifold?
Third, as MadMikeyL said, the oil light IS concerning...was it on before you replaced the manifold and if it was, are you sure it had the correct amount of oil in it?
And finally, I'm hearing some chug-chug noise that I would associate with something worse than a huge vacuum leak. Something that might come with the effects of not having enough oil.
I see you posted 10 days ago and haven't responded to any of the posts that were left for your benefit. I guess if you don't respond to this one that you either forgot about posting here or you resolved the issue you were having. In either case it would be beneficial to know what your status is on this car.
BTW, I re-sealed a Doorman manifold on my 96 using new seals and had no issues. It was leaking coolant into 2 of the plug holes causing misfires. Re-sealing took care of the issues. The previous mechanic either didn't remove the old OEM gaskets or thought the Doorman needed them, which it doesn't since is has seals built-in and requires no additional gaskets to seal to the heads.