Hi Just down the road from you 15/40 works fine all year round, While you have a chance dump a lot of water on the windshield, and sunroofs (sunroof 1st). Then check for water in the cabin drivers side right along the door and passenger side under the carpet. For the sunroofs the water drains behind the tail lights, the front at the door frame area underneath ideally there should be none if everything is closed up

Transmission is just a service unless you are having issues fluid and filter.

Check your front drive shaft it should have 4 or 5 grease points if not it will likely need to be replaced soonish - about an hour to swap it in the driveway

PCV breather on 03/04's it is a permanent deal but it clogs there is a sticky for a mod to get rid of it and use an inline but it is hard to get the pressed in unit out. Until then a bit of carb cleaner down there, once a month will stop blockages

As you are in Vancouver check these guys out Roverlanders of BC

@Dave03S good point on the warning lights but in BC at least, that is a chargable offense. The provincial insurance agency and RCMP take a real dim view of that sort of thing.