Specifically it was the wild grass pollens they were suffering with so its only a problem for the few weeks when they're in season.
Last summer I worked a 230 on a day when grass pollen was at its worst, I remember looking out the back cab window at line speed on the Bidston to Hawarden Bridge section of the line and seeing a huge plume of "smoke" behind us. I was concerned, until it suddenly stopped, then carried on a bit later on. I realised it was actually the train blowing huge clouds of pollen off the long wild grass at the side of the line, it's not present for the whole length just certain stretches. I've never seen anything like it at all.
Bearing in mind the 230s had sealed windows then and no opening cab windows, by the time I got to Shotton on the return from Bidston - as a hayfever sufferer, I was in absolute agony with bright red swollen eyes and sneezing to the point I abandoned ticket duties and focused on station duties hoping to get back home as quickly as possible!
I can understand why small radiators would become blocked, the amount of pollen being blown off was insane. For the pollen season last year the 230s did ok because they had learnt from the previous year and came up with some solutions to clean them.