How to clean a favourite old Raincoat?

[Mr B]

I have a dark blue bonded cotton raincoat that's a little over ten years old, fits me like nothing else and can't be bought anywhere these days.
It's grubby around the collar and cuffs and pockets and could really do with a 'deep' clean (I'm willing to fully reproof it afterwards). I've just had a few split seams repaired on it, but now it needs a 'detail'.

Have any of you gently cleaned a coat like this before?
Even though we have a modern large-drum front-loading washer here, I think machine washing it might introduce permanent crease marks into the fabric.
I'm wondering if there are any specific laundry products or techniques the good Salon might recommend?

ps
My experience with Dry Cleaning this coat leads me to assume it is merely hung outdoors by the Cleaner for 30 minutes and then hung on their rack after being wrapped in polyethylene.

[Mr B]

Ok, so it looks like soaking it in the bathtub might be ideal - Barbour Jacket Reproofing | Garden and Gun

...whilst GQ are just bending over backwards to offer reassurance and detailed advice - How to care for your raincoat | GQ