I just acquired this 82 240d. It runs fine at 126k. To avoid future fuel problems I bought a tube of Diesel Doctor ($5). The instructions indicate that i should use it for every 10 to 29 gallons. Seems excessive and wasteful if i use a tube at every fill up. What do you guys recommend? could i use something else and still avoid fuel type problems?

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$500 1982 240d owner "Gunter"
125k miles,4 speed manual
crank windows, MB Tex, all original
no a/c, daily driver
Scorecard so far....
$230 Maaco paint job
$27 dimmer switch, $40 shutoff valve, $45 brake MC, $260 calipers, $40 brake hoses, $40 side fender trim, $20 balancing, $109 lifetime alignment, $10 fuel return lines, $115 oil&fuel filters for next 30k miles