TB42 Welch Plugs

Hi All,
I have the motor out and changing gaskets seals and all general maintenance items, I found the Welch Plug at the back of the head very corroded so I am going to replace all the plugs. I know that they are not all water galleries, some are oil and not generally going to rust so cant imagine that they will need changing. Can anyone tell me which are the plugs I should be changing or should I just do them all. Any advice greatly appreciated. Also I believe there are 3 behind the inspection plate below the inlet manifold, do they require changing as well.

Hi Mick, make sure you go brass welch plugs and if the TB42 is like my 4.5 petrol there's 3 plugs I think against the fire wall 2 of them you have to take flywheel off .... have fun regards Alex