Sears wants 20 bucks just for a copy of the manual (SR10442)
OK I would check the locking mechanism.
and you say it goes back into cleaning cycle when you shut the door and lock it.
By never completing what do you mean, for instance leaving it on over night or a few hours.
Some of these older models have a 3 plus hour cycle. and it may need to run through an entire new cycle if it was interupted before completion.