Hi everyone!

This is my first post to the forum- my girlfriend owns a 2015 Micra (SV Trim, 1.6L engine, 4-speed auto transmission) and I am the lucky lad who gets to maintain it for her! I want this car to last as long as possible. I've been wanting to do the transmission fluid and spark plugs on it since I don't have any record of those being done before.

Would I be at any risk of the transmission slipping if I change the fluid at 140,000 kilometers? I watched a video on how to do it, tried accessing the fill port by taking out the coolant tank, battery, etc. and the stupid wiring harness is so tight I literally can't move it out of the way to even get my hands on the cap, let alone getting it off with a screwdriver (since I don't have whatever tool Nissan wants you to use).

Has anyone had their transmission fluid done at a mechanic? If so, what mileage was it done at and how much did it cost? (I'm from canada but willing to take answers from anywhere). I want to do it myself but it's genuinely so frustrating not being able to get access to the port that I might have a mechanic I trust to do it for me depending on the cost.

Hoping to get some insight from some higher mileage owners or anyone with experience getting the fluid changed.