Further experimentation on Audi A4 headlights that always die

2000 / a4 / 1.8 / red / cool looking
Well, we've all pretty much ascertained that replacing both bulbs at once for some reason keeps them going, and that replacing them one at a time
results in a bulb replacement every 3 thousand miles (or less!!!)
I can vouch (and have several times) that /that/ works.
But as an experiment, what I've done is save the "survivor" bulb for later. When ~1000 miles ago one of my bulbs went, instead of replacing both, I used the survivor from the past.
Now my car has, in theory anyway, two beaten up used but working bulbs in it at once.
I'm wondering if there is some impedance issue that will keep these two alive longer than one new one and one old one.
1. Anyone with any electrical understanding of what's going on? 2. Anyone else attempt this already? 3. I will report back with data.
http://www.allexperts.com is a nifty way to get an answer to just about
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