Thanks both for comment. I thought that the vacuum somehow put the fuel pumps under a greater load and that could aggrevate the poor start condition. When I get round to it I'll replace the fuel pump valves that seem from the info on the site to be the best and lowest initial cost bet.
As an aside, you folks are really fortunate in being able to get MB parts and accessories so cheaply. I have ordered the CD rom from the shop. In the UK it is "only available to dealers". Our parts prices here are astronomic; weird really given the Common Market, no duty from Germany to the UK. Maybe all MB parts are made in the USA!
1988 300E 128K