Sennheiser don't offer ventilated earpads with any of their headsets - it might just have been a Racal thing. I actually fitted a pair of scrap Sennheiser earphone speakers to an Astrolite and the sound quality is much the same as with regular Racal parts. The fact that the donor Sennheiser set was in a state beyond repair speaks volumes for their longevity and robustness (or rather lack thereof)!
I think all CAA/NATS units used Astrolites, plus some other airfields (LBA and BRS). Everywhere else seemed to go for the Airlite 62, twice as heavy but half the price. And still in production.