Wayne, thank you for this explanation.
A local collaborator gave me Symphonic Cleaning Fluid (American Inkjet Systems http://www.americaninkjetsystems2.com/support/how_to_use_symphonic_cleaning_fluids.html
) that is apparently a prophylactic treatment for clogs. The fluid, which is purported to be a potent solvent of dried pigment ink, is apparently applied to the capping station rather than directly to the head itself "3 times each week" to prevent clogs.
Your mention of Windex reminds me to ask how you'd apply it on a 4900. Are you apply the Windexed paper towel to the head directly, and if so, how do you access the head if I may. I'm sure others know this already, so I hesitate to ask.