I had the injection pump rebuilt about 10 years ago and the mechanic at that time mentioned that some of the one way valves in the injection lines were damaged. Perhaps they have got worse and are letting fuel drain from the injection lines. Does anyone know where I could source these valves? I think the MB Part No. is 0000741715
Unfortunately, these return (one-way) Bosch valves are not produced any longer, and they are very difficult to find, and when some are for sale, they are very expensive.
I was lucky to find a set of 6 last year, which I am keeping in my stores for the day I need them.
But check on Ebay - sometimes some comes up for sale. There are two types for early and late injection pumps. So make sure you get the right ones.
A work-around compared to replacing the return valves, is to use the cold start valve (CSV) for 1s, even if the car is warm or half-warm. Bosch produces a replacement thermo-time-switch, which works exactly as the original VDO below 35C coolant temperature. But it also has this extra 1s function, when the engine is warm or half-warm, and gives an extra fuel boost with the CSV. This gives the you an extra start aid and get the engine going easier, until you fill the injection pipes with fuel and get the vapors out, if the return valves are leaking.
Actually, if you look in the BBB, you will find that MB carried a retrofit kit, with the comment that "when the costumer would complain about difficult start at half-warm temperatures", this kit would be build into the car. Here they used a 1s relay and extra wire-harness to overrule the thermo-time-switch, and always give at least 1s boost with the CSV. You can still find these 1s relays for sale on Ebay and other places, as well and make a wire hardness and couple it into the CSV relay.
Good luck!
