I've done the cooling system work myself and think an experienced mechanic should be able to do the water pump, thermostat, replace the two cross over pipes, valley pan in 4-6 hours. Nothing tricky on the m62, just lots of bolts to turn. Put them into baggies as you go, label them and it's easy work.

I agree with the comments above - there's only two ways you can own a e53. Either $6k repairs don't bother you (financially and emotionally) or you learn/enjoy the DIY route. They require maintenance and few shops will do it cheaply.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles