This video shows how to fix the “foam in vents” problem and repair both of the HVAC blend doors using port plugs for a Porsche 911 (996 and 997) and Porsche Boxster/Cayman (986 and 987.)
Parts and Tools:
DSP Blend Door Foam Fix for VW Golf Jetta Beetle Passat: https://www.ebay.com/itm/DSP-Blend-Door-Foam-Fix-for-VW-Golf-Jetta-Beetle-Passat-/174723283813?
Nashua 361-11 Foil Tape: https://amzn.to/3tnoxob
Permatex RTV: https://amzn.to/3rfe8bq
Milwaukee M12 Oscillating Tool: https://www.homedepot.com/p/Milwaukee-M12-12-Volt-Lithium-Ion-Cordless-Oscillating-Multi-Tool-Tool-Only-2426-20/203111676
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I would not suggest this method at all when you can go in through the heater core in the front and not have to hack your vent open and tape it shut. That method allows removing a blend door completely out and properly fix it instead of having to cut the oem unit into pieces.
Don't do this to your porsche 986 or 996.
The plugs are a good idea though, unless they fall out inside the ac module and block the door.
2001 996 C2 here. Wow. Many, many thanks for such a great fix. The plugs make this so much better than using duct tape. Got my plugs from DSP via eBay in about three days. A little fear and trepidation before I fired up the oscillating saw and cut into the duct, but that was perhaps the easiest step. (And I must say, the first person to cut into the duct in this way was either a fool or a genius. I can't imagine he/she knew with certainty that the doors would be accessible once the duct was open. But they are.)
Cleaning the remaining foam and its degraded adhesive backing was a real pain, since it is ON BOTH SIDES OF THE DOORS. So you have to stick your fingers through the holes and sort of wipe off the backsides of the doors. It feels like a real victory when you pull out a piece one inch square. By the way, once the duct is cut, the opening is only about 3" x 4", so if you have big hands good for you but you won't want to try this fix.
Once the foam is gone, the rest is quick. The plugs are fairly easy to place and once the sealant has set you can turn on the fan, actuate the doors, and watch the remaining bits and pieces of foam fly like snow out of all the vents.
It definitely affects 987s as well. Both of mine have had it.