One of the welds has cracked on my exhaust where the 421 system goes from 2 into 1 just before where the 1 section clamps into the exhaust can.

Do i need to find somebody with special welding equipment to reweld it or can I take it to my local garage to fix.

Also does it matter if its stainless. Does stainless need special tools????

Stainless requires the correct stainless wire if Mig welded or the correct Tig rods.
If you can use a mig, then all you need is to change the wire. If you need it Tig welded, take it to someone who does this regularly. Tig welding takes a bit of time and a steady hand.
Tig is a neater way to do things, but the mig will lay down thicker welds. If you are unsure, post a photo so that we can tell you what kind of welds you already have.

Can you make it here Jos? If so I'll pick up a roll of stainless MIG wire and have a go for you.

P.S. you can weld stainless with mild wire and this is what a local Shit-Fit would probably do but the weld would then rust.

Using steel wire will work, but it also would be a weaker weld aswell as the rusting.
For a longer life weld, I recommend using the correct wire.

yeah probably andy. Thanks for the offer. Dont get the wire just yet, because I'll ask a couple of local garages first, but I may very well take you up on that offer