Fitting new caps and rotors required removal of the heater ducting on the left side of the engine bay so I also remove the heater blower motor and took the opportunity to remove the inlet manifold on that side and clean it out (the right side had already been done). Here's a photo taken while I was doing all that:
Just like earlier in this thread the manifold had a good amount of oil inside it which I cleaned out and then re-seated the manifold so that it was nice and leak tight. This should stop any minor leaks coming from there. Then it was time to get the distributor caps off. As you can see below with twin distributors, twelve plug wires and two coil wires it's a bit like spagetti junction so taking time to label everything up first with a marker pen is essential if it's going to go back together correctly:
The secondary distributor on 964s and 993s is driven off a small toothed belt so this is a good time to check what condition it's in. I'm happy to say that it looked fine as this has been nagging me for a while. If it breaks you get an immediate loss of power at the top end and can cause damage to the engine if it's driven for a long time with a broken belt, especially if the rotor arm stops on a particular pole causing the affected cylinder to be constantly firing.
The old distributor caps and rotor arms were well past their sell by date as can be seen from the pics below.
Some say that badly worn dizzy caps (like mine) will lead to a loss of power. From the test drive after fitting the new parts I would tend to agree with this as the engine feels a bit more lively. But more importantly I'm glad to have those old caps off which I guess could have lead to misfiring.