Exhaust manifold

Yo!

(Finally) got The Fun back from the garage with a new MOT and service (7 bloody weeks after it went in!). They have said that the exhaust manifold is cracked, but seals itself once it's up to temperature. (The use that she'll get means that running temp will be reached quickly and maintained for some time) Given that this seemed like work generation, I told them to leave it, as I did actually want the truck back at some point.

I've found an exhaust kit (inc. gaskets etc), how easy are these things to change over? Is it actually worth doing?

Cheers