Can't I just replace the Immobiliser? Why do I have to go to the dealership?

[Qmulus]

There are lots of threads on this, but I will summarize.

If you get water under your driver side seat, don't wait until the alarm/immo module starts malfunctioning, but rather disconnect the battery ASAP (MOST IMPORTANT to stop corrosion) and remove and open the alarm/immo module and dry it out, preferably with compressed air to get the water out from under the relays. That is where the worst damage is done. The longer it is wet with power applied, the worse the corrosion. If things are not working, just drying it out will not save it. The corrosion damage must be repaired and damaged components replaced.

Replacing the DME, Immo and key transponder "pill" with the parts from another car will get it working, but is a BAD idea in my opinion, as your car will now have the electronic ID of the car those parts came from. Therefore, you will not be able to program new keys or replace any of those components as the programming codes Porsche has for your car will no longer work. So, basically you just changed your car's electronic VIN to that of the car those replacement parts came from.

What is the "correct" way to fix this? Well, you can get a new immo/alarm from your local dealer for $500-$900 depending upon the part number, and have the dealer program for $150 or so, or you can get it repaired, or get a replacement used alarm/immo module and get it "cloned" to match your original. Note that you really must have the exact same part number and sometimes also software revision for this to work.