It seems that the transparent plastic cover which covers the speedometer, rev counter etc is stained from inside and i'd like to give it a good clean. Even the clock cover seems to be a bit stained (i guess due to the previous owner who was a smoker) from the inside. Do I need to remove the whole dash to get hold of these two covers from the inside?

i think you may just have to remove the whole dash to do so - in the main club under the guides section there is a guide on how to remove the whole dash unit to get at them

here you go http://www.club323f.com/ba/tuning/dashr ... emoval.php

I discovered that most of the stains are external. However i cannot remove them with water. Is there a safe way to try to remove these clear stains without damaging the plastic?

some interior cleaner should do the trick, i normally use Armor-all which seems to do the job.