adivce on how to replace a SUMP & MOTOR ASSEMBLY on a kenmore dishwasher

I decided to replace a sump and motor assembly on a kenmore dishwasher (model # 668.16879000).
I ordered the part through sears.com (their part # 8534884).
The black seal on the new sump assembly looks different then the original seal. Also the seal is molded to the assembly.
My problem is that I cannot get the new part to properly seat in the dishwasher. I was told by a service tech that you should libricate the seal with dishwaser detergent prior to installation.
I did this, but no matter how hard I push the unit (from the inside of the dishwaser) I cannot get it to snap in place. There is only one way (I hope) to fit the part (A key on the part fits into a slot in the bottom of the dishwasher) , so I do not think I am putting it in wrong. I would appreicate any advice on the proper way to install this sump/motor.
Thanks
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I don't know if this applies to you but I've twice gotten the 'correct' Sears part and it wasn't right. The part numbers were just fine - what I received matched what I ordered but what the parts list said to order was not right. I got vacuum cleaner belts (for the beater brush) and door gaskets for a dishwasher that didn't fit and were clearly wrong - though at first glance they looked OK.
t wrote:

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