Intake manifold gask

I am chasing a vacuum leak on my 2004 S-Type with the 4.2 engine. 85,000 miles.
I have taken the intake manifold off to replace the gaskets. I have got the lower gaskets but cannot find the seals that go between the plastic manifold and the aluminum risers. I have not separated them to check the condition but figured as I have gone this far I should replace everything.
Any thoughts on suppliers would be appreciated.
Do you use a gasket sealer when installing the assembly and are there any tricks to getting it all together.
My arthritis and age keep getting in the way!!

I generally get stuff like that from and remember that engine was also in Ford Thunderbird and Lincoln LS so your local parts store may carry them though at a higher price than Rock but lower than the Jag dealer.