The last week or so the transmission has been a little slow when cold going into reverse and then drive ...... then a couple of days ago it started flaring changing into 3rd then dropped into limp mode. I was 1 minute from home so I limped home, turned it off and restarted it and it was fine although still flaring into 3rd.

I check the fluid and it seems fine, it's still flaring into 3rd ..... Has anyone got any ideas, it's a 5 speed tippy.

Check that the heater core isn't leaking coolant onto the ECU

Yep as above the same thing happened to me about a month or so ago. The relay above my left foot area had gunk on it. Replaced it all good. But then found the coolant in the footwell and had to get the heater core fixed.

How many klms has it done?

280,000kms

I think the screen needs to be resealed as it's been leaking badly on the left so that could be it.

280,000kms

I think the screen needs to be resealed as it's been leaking badly on the left so that could be it.

Unless you have rust on the left side of the windscreen, it's unlikely to be leaking. Look at the air intake inside the plenum chamber - need to remove wipers and leaf guard - and check for rust there or a build up of leaf litter. Also check the heater core, if the carpet is wet, smell it for coolant.
Check the ECU for external moisture.

Sounds like the clutch packs are worn out.

Unless you have rust on the left side of the windscreen, it's unlikely to be leaking. Look at the air intake inside the plenum chamber - need to remove wipers and leaf guard - and check for rust there or a build up of leaf litter. Also check the heater core, if the carpet is wet, smell it for coolant.
Check the ECU for external moisture.

Done all that and it only started leaking after I had a new screen installed. National Windscreens are coming out tomorrow to replace this one(lifetime warranty) and do a better sealing job.

I had the same leaks happen when I replaced the screen in my old TH and they had to come out and reseal it.