I've got the same kit to replace the battery in my Formula 1, it's probably not waterproof any more because the rubber around the bumpers has almost fully disintegrated so I'm not too worried about it. That said I do plan on getting a new o-ring and lube to help the case be sealed.
I actually got a battery and watch service kit off Amazon.
Peanuts and figured it would pay for itself.
I don't need it to be sealed as I don't use it to wash up.
Speaking of which my 2000 series needs a new one again! Better get onto it...
(Although I'm strangely addicted to the 5 second sweep)