Product review (5 stars): I decided to replace the belt first and it's like having a new clothes washer
This is the replacement belt for the Whirlpool Duet GHW9400PW1 as supplied by Whirlpool's parts supplier "marcone".  I did order through Whirlpool because there is confusion on the Internet sites about which belt is the correct replacement.  Today I installed this belt and it works perfectly.

My Whirlpool Duet was presenting a Fault Code F6, which many people suggest is a Motor Tachometer error, and the first recommendation is to replace the Motor Control Unit (MCU).  That would cost about $75 for the service visit and another $150 and up for parts and labor.  Because my unit was seven years old, I decided to replace the belt first and it's like having a new clothes washer.  The repair is easy if you have the socket to remove ten screws on the rear, swap belts (the drum will move enough for ease of install) and the total job takes about the sme time as cleaning up the floor behind the washer and dryer (while you getting the dust bunnies evicted).  It takes longer to run a test wash load than to do the repair, and it's an easy DIY project.

I do wish I had known this was the belt I needed, as I would have saved $25, but I'm pleased I avoided the repair call and a significant wait for service and the added costs.

I was curious that the belt is marked "Made in DE".  I don't think that's Delaware, is it?