A good window tech should be able to re-use the old seal. I just replaced my glass after being told I'd need a new seal. BS; I went down the street to a SafeLite installer and without any issues, had the windshield replaced (without a NEW seal btw.)
If you do have to replace the seal, be prepared to locate a Bar and have a couple of drinks.
The seal is not cheap and AUDI is the only vendor, I was able to locate in my area (Houston.)
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