Mixture screw o-ring disintegrating!

A few weeks ago I had an idling issue which was caused by the mixture screw o-ring breaking down and causing a blockage which would stop the car from idling altogether. Before, I just assumed it was because I had used too much carb cleaner and it had eaten the seal but once again on my way home from the agm it decided to do the same thing and surprise surprise I find the o-ring is starting to disintegrate! Could it just be the ethanol in the fuels im using? or maybe the heat of the engine? but none of the other o-rings seem to have the same issue

Does anyone else have the same issue?

Cheers,
Matt

Also does anyone know what size the oring is that I need for this?

Im starting to suspect that heat is causing this issue as I removed the heat sheild from underneath the carb before this problem first happened