Engine Missing and other weird shite!

[sleekism]

My Fairmont has slowly been developing a miss and is now at the stage where it will miss badly under load i put some injector cleaner in and it helped a bit but it still misses pretty bad going up hills with the occasional shudder at idle as well. It has 135,000 kays on it.

My parents have a series 2 VCT XR6 and they have also started to develop a miss though are not at my stage yet. They hav 128,000 kays.

Am I right in thinking this is the leads? What about the coil or fuel filter?

Also what the hell oil do you put in the VCT? Mine says 5-30 on the filler cap and the manual says 10-30??