Yes, bio-diesel will do the job. Instead of purging i periodicly buy 5 gallons of B100 and dump it in when its close to R on the gauge. Then Rev it up good on the highway. (itallian tune up). It works wonders.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes