looking at Mircocat its not available as a part,

What is its purpose, is it important? Do I need to replace the whole propshaft connector to replace it? 2004 L322 V8

The rubber boot/gaiter protects the CV joint from dirt ingress. If it's split or holed then dirt and water can enter which will lead to wear, corrosion and failure of the joint. It will need fixing.
Unfortunately, as mentioned above, the rubber boot is not available as a separate item and I can't see any aftermarket replacements.
It will need taking off and checking for any wear or damage to the CV joint, if it is worn then it will need a new shaft anyway (CV not available separately although a prop specialist might find a replacement).
If the joint is OK then small splits in the rubber can be 'fixed' if cleaned up and superglued but there is no guarantee on how long they will last, I've done that before as a temporary measure until I could replace the boot.
You might be able to use a universal CV boot clamped on the outside. The front prop doesn't move with suspension like a normal driveshaft so should stay secured.

Last edited by Weejock on 2nd May 2016 2:06pm. Edited 1 time in total

Definitely something that needs fixing if cracked. I've just had to replace my CV joint and drive shaft as it lead to excessive play and very vague steering. Tom

Current Drive
2011 4.4 TDV8 Autobiography - Santorini Black - Ivory Leather

Previous Drives
2004 Model Vogue Td6 (Touchscreen) - Java Black - Parchment Leather
1994 RR Classic 3.9 V8 Soft dash - Niagara Grey - Grey Leather
1972 Series III SWB Safari - Green (Hand Painted) - Black Plastic