An Update.
Finally got the plugs out
.
All drained down and refilled.
Remembered that the car needs to be level so did a bit of a faff with a couple of jacks and a spirit level.
I reckon that the oil in there had been there for 19 years and while it wasn't horrendous it wasn't great. I'm sure that I put more in than came out
.
The changes now feel better and the car seems quieter - or maybe that's just my duff hearing
.
Thanks for the help guys.