I have seen the situation where the fuel leaks out of the control piston in the fuel distributor. There is no seal on the piston other than very close tolerances and after many miles the piston can leak - which is not really a problem since the fuel simply evaporates and gets inhaled by the running engine. It might explain the leakdown pressure problem.
However - I dont think the leakdown problem is causing your long cranking times. When the fuel pump is started, fuel pressure is almost immediately at maximum. It does not take more than 1 second to reach maximum even if the accumulator is not pressurized.
Can you verify that the fuel pumps are indeed running when the problem happens? I had a similar problem and it turned out to be the fuel pump relay. There were micro-cracks in the solder joints on the board. It could have caused low voltage at the fuel pumps. Anyway, I resoldered the board and everything is fine.
You can build a poor mans fuel pressure tester by getting an old fuel line with the appropriate fitting and welding a pressure guage fitting to the other end. Install a 0-100psi guage and you have it. There are two places on the fuel distributor that can be monitored for pressure. Buy a fuel line from the local MB place and modify it.
Proceedures for testing leakdown rate are on the CD.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k