Please excuse me if I am over-thinking this, I have not owned an auto before, and spent too much on this to think "Meh, it'll be alright" without knowing for sure.

I used a little spirit level on the bottom of the auto oil pan, and it was not quite 'in bubble'.

The running boards however were perfectly level.

So I guess what I am asking is - just how level does level mean (I assume there is some leeway), and measured from where?

Thank you!

The way I did it was to use a torpedo level and go right off the bottom of the oil pan on trans. There isn't a large difference between the side rails and the pan and it won't affect the amount of fluid to where it would cause any harm. The biggest factor is to make sure you check the level of the fluid while the car is idling. If you check it with the engine off it can cause you to be 2 to 2.5 quarts low. I was shocked that there was the much difference but there was. I have seen more people do this. I always do a full flush as well, never been a fan of just draining the pan and adding just the fluid that drained out. Make sure you go through all the gears letting it idle a few seconds at each one. This will flush all the fluid through the valve body and it holds more than you would think.
NCH

Thank you mate, that's good to know.

Yes I followed the excellent write-up on this site, it all went very well, I had a bit of a cock-up when finishing off with checking the level, but that's my fault (Forgot to replace the level plug washer with a new one, and took it out with the engine off by mistake! It only lost about 10 fluid oz before I realised what had happened and quickly got the new washer on, I will re-check the level at some point though)

Good to hear and at least you won't make that mistake again, lol!!!! Glad you caught it before you lost to much fluid. Its things like that why I refuse to let anyone touch my vehicles with a wrench. Mistakes happen to everyone, but if you would have had a shop make the error you may not have noticed until a failure had happened and a new trans isn't cheap. If I'm going to blame anyone I would rather it be myself. Later
NCH

Totally agree, I work in construction (So I don't mind working with my hands) and when I see the endless mistakes "professionals" make (And get away with).....

As you say, it's not about not making mistakes, it's about how you deal with them.

Later!

If your garage floor is pretty much level that’s good. If it’s out of level by a 1/4” you’ll either be short or too full by probably a table spoon or so. Haha!

Not a big deal.