Alarm (immobilizer) Unit

[clb0099]

Ok, so here is my question. I was in contact with a guy who works on Porsches and I told him that my immobilizer might have gotten wet and might be causing me some issues. So I asked him if I could buy a used one on ebay or at a junk yard.He stated if I did buy one somewhere that I need to have the vin # from the car it came from. Now my question is this one is this true? Also if I did find the Alarm and got the vin # with it to from a legit place could my keys be programmed to work with it. Also would I ever have a problem ordering more keys now that my immobilizer had another vin # associated with it. Or is the vin# needed only to access the immobilizer to re-program and load my correct vin #. Please let me know what you think.