My shop manual says to wet the windshield when you do a wiper motor test. You can't expect to sweep dry rubber across dry glass without resistance. For a true test, get out the garden hose and see how it performs. If it is still sluggish, get out your wrenches. Otherwise, wait for the next rainstorm.
No matter what the results, you might as well give it a wash while you're at it.
Bill
