Servicing control pressure regulators (aka WURs)

Curious to know other people's experience with this.
After my car was lying idle for some months during a protracted repainting operation, I had difficulty starting the engine and a quick test of the control pressure showed it was too high. So I decided to strip both regulators completely and service them. I also decided to implement the fairly well known modification for adjusting the position of the bimetallic strip locating pin, to allow fine tuning of the cold control pressure.
I had previously had starting problems on one bank and found that the inlet filter on the WUR was blocked with crud. On that occasion I had just blown it out with compressed air which solved the issue at the time, and did not attempt to remove the filter screens.
This time round it was a full stripdown, so the screens had to come out. (That wasn't as easy as others have described, they were well jammed into the bore of the 10mm fitting.)
Image Unavailable, Please Login Image Unavailable, Please Login I found in each bore five separate screens, two coarser screens of approx 8.5mm OD and three fines screens of approx 7.5mm OD. Each bore had a significant quantity of green powder (relative to the mesh size). In other descriptions of this filter pack I have seen mention of fabric filter disks. Mine are definitely a very fine stainless mesh, as shown on the pictures above.
My first question- anyone know the likely composition of this green powder, and what can be done to prevent a repeat occurrence?
My second question is- what is the point of these filter screens? The way they are manufactured and fitted means that they can be bypassed by contaminated fuel. The pack of five screens cannot be compressed by the banjo nut to form a seal (because of they were, there would be no crush on the copper sealing washers). In any case there isn't a flat land at the bottom of the threaded bore which they can seal upon.
I was tempted to leave them out altogether, but eventually I made up a punch to punch out four new screens from stock material, and made up two sandwiches of five disks, comprising two of my new screens and three of the recovered and cleaned fine screens mentioned above. I probably wasted my time, becuase the clearance around the periphery of the filter disks is many times greater than the mesh opening on the fine filter screens, so I can't see the thing working effectively in any case.

The third question I have relates to the balancing line between the WURs. I'm a bit sceptical about the effectiveness of this. At the very least it confuses trouble shooting. If I understand it correctly, a blocked filter on one WUR would cause the control pressure to rise and the mixture to weaken on both banks, not just on the one with the blocked filter. I would have expected some form of flow restrictor in this line or some other mechanism to minimise this effect. Has anyone tried running the engine with two entirely separate and isolated systems?

 

Thanks raemin for the information. The 928classics document is one of the best I have seen on the topic. And I'm looking forward to making up some B12!
Yes, I believe the deposits have something (everything?) to do with the ethanol. Most of the fuel we get here is E5. What bothers me is that the deposits shown on the pics I posted above have accumulated in less than 18 months after a complete clean out of the fuel tanks, fitting new hoses and filters between the tanks and pumps, fitting new accumulators and new fuel pumps and filters. Back then (due to a cold start problem) I also had to clean out the WUR filter (just one blocked) using compressed air and cellulose thinners, and here I am again after 18 months (with zero kms driven) and with more deposits. The car has been stored indoors and not driven.
These deposits should presumably be trapped in the in-line fuel filter after the fuel pumps. So are they forming somewhere between the fuel filters and the WUR? It just doesn't make sense to me.
Given the way the filter pack is constructed, I'm not convinced that soaking it in B12 would be a long term solution.
By the way, the deposits have a distinct light green colour, just like verdigris (copper carbonate), rather than white colour you mention.
I'm getting paranoid imagining all sorts of chemical reactions taking place!
Pat