Originally Posted by whitneyd
If it's on an Escort Cos it's because more than likely your engine mounts are shot. So when you engine torques it tries to pull the CV apart slipping the boot off enough to let some of the grease out then the engine settles and pushes the boot back on. This happens when the straps aren't tight enough and I believe one of yours looks like a zip tie. That's a no no.
You might be on to something there - but I am wondering (looking at the pic) if the boot is rubbing on the chassis leg, rather than the clip being pulled off then put back on. They are tight and I just don't think it would go back on. Perhaps the small one could move, but it looks like the grease is from the big end.