CIS fuel distributors are precision instruments and as such do not tolerate contamination well at all.
as an aside, I cut open a 70,000 OEM (Bosch) fuel filter on a volvo I just bought. There is a very long roll of filter media in there. I would be very surprised if the fuel filter would be the source on a BOSCH, Hengst, Mann or other european OEM supplier.
Contamination source will be the key to the direction you go.
1) if it's fuel varnish (not driving it for a very long time). Fuel system detergent might work, but a teardown is probably the only way to be sure.
2) if it's the distributor itself self destructing, then a new or known good used distributor is the only solution.
3) if it's upstream (either the filter self destructing or letting contamination through) then at a minumum a teardown is necessary to evaluate if the distributor is permanently harmed (scoring, rust, pitting...).
Some line flushing, new fuel filter and new fuel injectors will most likely be called for also. Please be careful. working with that much fuel exposed in a a confined space is bad news.
S, J.R. Brown
2000 G500 LWB Obsedian Black
2005 Toyota Tacoma Access Cab Off Road Sport
1993 Volvo 240 Sedan Anthracite
1980 450SEL Champange (owned it for 15 years. Great car)
1986 280GE LWB Anthracite (Sold it and kinda wish I hadn't)