This is probably because of modern fuel additives & the introduction of ethanol into fuel. Repair kit for a four cylinder alloy Bosch. This Repair Kit is suitable for the following Bosch Fuel Distributors numbers.
Repair Kit for Bosch Fuel Distributor 0438100088 Mercedes 380 SL/SLC Roadster
Repair Kit for Bosch Fuel Distributor 0438101018 Mercedes 500SL 560SEL R107/W126
0438101012 Repair Kit for Bosch Fuel Distributor Mercedes-Benz 190/260/300 E/CE
0438101016 Repair Kit for Bosch Fuel Distributor Mercedes 560SEC 500SL R129/W126
0438101044 Repair Kit for Bosch Fuel Distributor Mercedes 300 CE-24 300 SL-24
0438101026 Repair Kit for Bosch Fuel Distributor Mercedes 180/190/200/230 E/G/TE
