I tell people budget $100/mo you should be able to keep e53 in very good order. Starting with under maintenained budget maybe $800-1200 off the bat. I wouldn't preemptive change suspension stuff but the coolant stuff preemptive for sure.

Wifes and my 01 both had CPS fail 133 ± 3000 miles and disa valve both failed 160-170,000. Fuel pump 130-180,000

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)