I have an 03 Z4, never joined one of these sites, but have had many problems with my Z4. I have taken advice about window regulator problems, steering notchy issues, and the latest being my boot constantly being soaked through and the battery compartment filling up.
I finally decided i needed to at least say thank you. I came from reading a post and link from the Z4-forum of someone called wondermike from someone called sixspeed here. He posted a link here on how to unplug the drains. I was losing sleep up until today when i got to try it out. I followed the instructions and found lots of crap in my BLOCKED offside (drivers side UK) drain. I spent about 4 hours in total with my dad (he is still a hero) clearing out both sides drains. Thank god my near side seems clear!
I obviously need to test for a few weeks to be sure but the fact that the drain on the offside was completely blocked and now runs clear makes me 99% sure this is going to fix the problem that has worried me for weeks! Whether he/she sees this or not, I felt I needed to write my absolute thanks somewhere and advise those others that may be in the position i was 10 hours ago, that this may really be your problem, and this is THE fix.
THANK YOU SO MUCH!!
One thing i will add is that I used electrical cable to poke at the obstruction from both ends (The stuff that is usually insulated throughout your house). Perfect flexibilty with adequate strength. I unfortunately had no compressed air.
Also I think the design is very clever. The exit of the drains are small, and they are strangely shaped, but they limit any rubbish coming up the wrong way, so even though they have caused me so much heart ache, i do realise the amount of design and development that must have gone into them.
God I do not know how I have written so much. I appologise and thank any of you who have gone all the way through!
Jiz