I bought my 240D new and have a WORD document detailing everything ever done on the car since Day 1. The WORD document is updated every time I do something on the car. It is easy for me to use and easy to search for when something was last done. In addition to that I also note in the service book when a routine service is done. I also have a record of every single tank of fuel and the mpg since it was new. That's 29 1/2 years' worth so far.

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles