Heads Up Advice Wanted before Opening GMT Case

[ETonePJ]

I have wanted to look inside my GMT 1675 for quite sometime. I've resisted that inclination, until now, because I would always recall my dad telling me, "only two kinds of people open a watch, watchmakers and fools."
But now, having owned this watch for 40 years, I would like to open it up.
I have two reasons for wanting to do this. 1) I'd like to see the inner-workings of my watch; 2) I hope to find any service markings that would tell me if my dad had gotten service on it before he gave it to me.

So, I purchased a Bergeon ball. I have used this to open a Seiko 6139, and a fake Rolex I got in Thailand nearly 40 years ago. Same kind of caseback, and the ball opened it fine (and it was resistant due to oxidation in the threads).

While I now have the means, I want to make certain I consider any precautions to prevent contamination or damage during opening and closing.

Any advice will be greatly appreciated.