If it comes to replacing the dispenser it can be done as a do-it-yourself project if you don't mind doing it yourself but there are some things to consider first.
You don't mention any problems with the soap dispensing and if the soap is dispensing then the rinse agent is mot likely dispensing as well.
The full/empty indicator is mechanical and is not run by voltage and if it gets stuck you can tap on the dispenser with a finger and it may free up. If it never moves at all then you would have to replace the dispenser assembly to fix the problem.
You should also know that the rinse agent is not dispensed in the quick rinse cycle. The water my flush some out but it doesn't actually dispense.
The image below may help with this problem. There is an adjustment that can be made to dispense more rinse agent each time. Check this and if the setting is on 2 then try adjusting it, as shown in the image, to a higher level. Too much might cause suds in the water.
The 2nd image shows how to access the dispenser to change it if necessary. Remember to turn the power off first.
As long as the dishes are coming out dry and with no spots then most likely the rinse agent is being dispensed. On the lower settings and depending on how many cycles are run each week it might take 6 months or longer to use all of the rinse agent.
The dispenser assembly 8558129 can be obtained from the following link:
. I suggest you do this yourself because with our help I'm sure you can and if you pay a repairman to come out and install the $40 dollar part you'll end up spending $approximately $160-$200 dollars to know how much rinse agent you have.
I hope this information is helpful to you but submit another question with any additional details for further assistance.