To Retrobright or not to..

[Oldsmobile_Mike]

I retrobrited my A500 and didn't put anything on it afterward, and it yellowed again.  Looked nice for a while, anyway.    My A2000 faceplate seems to have held up a lot better, but then again (1) it wasn't as bad as the A500 in the first place, and (2) I don't think I used such a strong mixture of the stuff.  Maybe there's some trick in doing it that way?

[Oldsmobile_Mike]

Is there a guide (ideally with pictures) of how to do RetroBright and apply it?

Not a good one.  I spent hours looking up this same thing when I did mine, with limited success.  There are plenty of guides, but most of them only mention stores and products that are only available in Europe.  Here in the US they were next to useless, I wound up having to "wing it".  As you're in Europe you might have better luck finding said products, lol.