Hi Andrew, pollen is very sticky and difficult to remove. I do clean my own sensors, but the kit needed to clean them yourself is not cheap and you
must use the correct fluid for your sensor - My D100 uses Eclipse One and the D3 and D700 use Eclipse Two - there have been reports of Eclipse One damaging D3 sensors. This
LINK I regard as the "Bible" on DIY cleaning. I use fluids and swabs when necessary and a rocket blower or Arctic Butterfly most of the time. If you follow my link you will see these are not cheap solutions. On this occasion I would go for a professional clean if I were you. Then I would save for a rocket blower which should see you through most problems in future.