Try to get a top rack from a KD19 or 20 model, they have a longer better performing top wash arm, you can use the rack from a cheaper model if you want it just won't have the height adjustment etc.

Be sure the person coming to look at and fix your DW has a new inlet valve [ and gray hair ] with them, this is very likely why it is under filling.

John 

Water valve inlet screen is plugged with deposits. It's a very common issue in hard water areas. The original valve is a dual solenoid but the new valve (part# 4171000/WP4171000) will be a single solenoid. Don't fret, it works the same. I highly recommend buying the valve first and having them install it. They will upcharge the hell out of you for the part.

A new top rack from an 18 well into the 20 series machines will fit. I'm not sure which model is the last but someone here should know. There is a difference between models though. The lower end models do not have the folding tines and height adjustability. The original KDS-18 rack has a smaller wash arm than the 19+ series, so a newer upper rack with be an upgrade which provides better washing performance. I have only owned TOL models (KDS-18, KDS-19, KDS-20) so I'm unaware which TOL racks from various models will work.

I would HIGHLY recommend replacing the seal and impeller! When these go bad, it will leak water down the motor shaft and take out the bearings. It will require a new motor which is extremely expensive now. This will also rot out your floor if installed on a subfloor. Here's an NOS seal and impeller https://www.ebay.com/itm/124047854609QUE...