Thanks Carl0s and williamX5. Valuable information.
Here's what I have come up with.
The LH side guides can be done without removing the cylinder head.
With the RH side, the head has to come off.
So be it.

After reading a few posts about the valve stem seals leaking I decided to
take the heads off both sides so I can take a look at these and replace if
necessary. The seals can be done without removing the heads if you have
the special tool, but then it is a lot easier to take a look at the seals with
the heads off. I know that you can check the seals without removing the
heads, but when you consider that one head has to come off, it's not too
big a deal to take off the other side.

It was easier to remove the entire engine to do this and along with the transmission. I was then able to look at the catalytic converters and these
look nice and clean.

So by tomorrow I should know if the valve stem seals are okay and
hopefully there are no other issues revealed when the heads are removed.

Although only one guide had the broken plastic, we could only buy a full
timing chain kit, so all guides and chains will be replaced, plus gaskets, head bolts etc. The original chain had some stretch in it. 150K kms (90K miles)

I had a problem with the radiator fan not working sometimes and then the water pump failed so the motor has been very hot on a couple of occasions.

A lot of work for a crappy little piece of plastic.

This all started because of minor oil leaks from rocker covers which leaked oil into the alternator and caused 'Low Battery' warnings which then threw up all sorts of other electrical faults. DSC, Seat belt tensioners and Air bags.

I have managed to cure one of these which was the DSC light on. This was a faulty Yaw sensor on RH side.

I won't know if cleaning the oil out of the alternator has cured the other
problem until the vehicle is back on the road. I replaced the regulator
on the alternator while we had it off as that was only $69.

I'll keep you all posted on progress.