Kitchen Large Electric Appliances - Soap residue in dishwasher

I have a Jenn-Air dishwasher that is about 15 years old. Lately there has been soap residue/particles on the dishes after the washing has completed. This is mostly on the lower rack. It seems to run through the various cycles without a problem and I have verified that the soap dispenser is opening up at the correct time. The holes in the spray arm do not appear to be clogged (and I can see that water has sprayed everywhere if I open it up mid cycle). Also, the water is somewhat hot as I would expect. The problem is worse with powder soap than with liquid. Any thoughts as to what may be wrong or is it just time to get a new one? Thx, Dave.

On the extension where the spray arm is mounted there is a small rubber check valve ,that may be worn out.The water shoots out of the hole instead of going to the spray arm.$2.00 shoul take care of it.Go to a parts place and ask to look at the parts break down. It will give you an idea .