Hello again Rod..
Thank you for your message.
I know what you mean re manufacturers but we have info that we have access too ( that we pay heavily for! ) which is what the makers have - but, with some "parts of the car"...ie, what you are after - the info is just not there.. they seem to think one doesn't need it I think! very frustrating.
However - I did say I would look further for you and I have come across a couple of pics on the net that may help you ... I will gladly share them with you..
Looking at the first one here you can clear see where they come out - and following back you should be able to trace the source - or, I would suggest - rake them out with welding wire or the like, from the lower openings - up. That will sort them if they are clogged..
Here's the pics for you..
The first one HERE
Second - HERE
. and an "overal" view - HERE
I hope they help you some more, they should as they at least give you the idea where to be looking..
Rod - I hope that helps... Please dont forget to click on the OK ratings for me - as thats how Im credited for time etc helping you .. Thank you in advance for that ..
Kind Rgds, MIKE.