Thanks for the advice.
I have found out why Haynes recommend it as a proffesional job.
One of the 6 bolts holding the sump is completely inaccessible without removing a serious looking bracket that appears to be holding quite a bit up.
I have drained the old dirty oil and refilled with fresh for now.
I had not read the last post so put about 4 litres in first then turned on engine and went through the gears in turn and back.
Checked fluid and it seemed to be on lower hole so put about 1/3 ltr in but checking it was impossible. Kept wiping Dipstick but oil was always way up each time I checked about 10 times. So gave up as about the same went in as took out so should be fine.
Drove it down road and not much improvement as far as holding in gear too long when cold but changes seem a bit smoother. Will take it out later for a longer drive and see if the clunking when putting it in drive has reduced or gone.
I might need to get a quote from a garage for changing the filter.
As you say do about 500 miles and get the old filter changed and fresh oil back in. I have the parts now so only labour is the extra cost.