I replaced mine with an original part from GW.  However, given the price I paid for it I would not do that again.  While the new cover fits perfectly the rubber (particularly the thin tab where it connects) is pretty thin and I can see it breaking again, especially with my grandkids using it.  After replacing it I found several complete systems - hose, head and cover - for not much more money and they seem to be a more durable design.  
So if this one ever starts to look like crap or gives up the ghost I will go the full replacement route.  
Hope that helps.