Tranny fluid question

[Slamtry]

I need to change the tranny fluid in my Classic. It has 145,000 miles on
it (and before you ask, yes it has been changed before).
I have two questions:

1) Is is likely to start leaking if I switch from dino to a synthetic,
e.g. Redline MT90?

2) Is there any point to this upgrade, given that I live in Southern
California, where I will not see temperatures below 50 degrees from years
end to years end. From reading the archives and the forums, it seems that
the main point is to improve cold weather shifting.

TIA

Dan Hugh-Jones