Although this is not vari-cam specific. I ran into an emergency situation over the weekend with an f900 sony series 3. Client was demanding alot of excessive playbacks.
Producer felt that money was better spent on Craft Service than a Video Assist person:( Eventually my prediction came true: the playback heads clogged!
The rental house did not include a head cleaning tape/I forgot to check for one when prepping. So I took off the side of the camera, took a clean cotton handkerchief from my kit, applied lens cleaner to the ‘kerchief and went to work on the drum and tape path, both were quite dirty.Slapped it back together and ran a quick test- Warning light stopped blinking/no particle breakup on playback.
Producer called today to inform me that the tape we were encountering problem with was fine!
Although the aforementioned technique may be frowned upon by other tech types; bottom line is when you have to make it work, you do it. The heads are sensitive, but durable.