I am electively changing out radiator, water pump, exp tank, thermostat, and associated hoses on my 2001 540i 6-spd. 83,000 miles. I'll install new AC and serpentine belts as well. I sure could use advice on 1) whether to change out tensioners / pulleys, and 2) whether, if yes, I should buy tensioner / pulley assemblies or just change out the parts with bearings in them (can't tell for sure from Bentley & other diagrams or online parts sellers if they're sold piece by piece or in assemblies). Thanks.