I have a good friend that has been shooting with me on a few jobs and has had problems with his XL1s and my Panasonic 63 minute MQ videotapes. Audio drops out and video stutters. I have suggested fast forwarding and rewinding before shooting. This problem seems intermittent. Whst would you suggest? Cleaning tape? Clean the transports? Different tape stock? Thanks.
Your friend's XL1S needs a cleaning. Suggest a reputable camera repair place in your area and have them do it. Tell them what's happening with the XL1S and they'll clean the heads and transport mechanicals. Have them check for proper transport alignment at the same time.
Try to avoid using a head cleaning cassette, as they are very abrasive and will decrease the service life of the heads substantially. That's how they work, by sandpapering the heads clean. If you must use one, follow the directions on the cassette to the letter.