I have been told that the rubber buffer on top of my rear shock has perished. Has anyone else had this problem and if so is it easy to change

Yeah rear bump stops are a very common service part. Not too difficult to do providing you have the right tools etc.

I went through the same with my Octavia, OK, it's a different car but the principles of replacement will be similar. My car...

 

http://www.briskoda.net/forums/topic/341314-octavia-scout-rear-shocks-do-i-need-all-new/?hl=+bump%20+stops

 

A fellow member also created a very useful guide for replacement here...

 

http://www.briskoda.net/forums/topic/364761-replacing-rear-suspension-bump-stops-on-octavia-2-lots-of-pictures/

 

Thanks guys for your help. I'll order some and get them changed