[Luxter]

First, welcome to the forum and congrats on your purchase!
It would really help if you knew what exactly leaks in your engine.
From my (limited) experience, I cannot see any oil leak fixed reliably for $115 unless your oil filler cap was not tight enough.
The "bigger" oil leak - if that is rear main seal (RMS), would cost much more than $545 as it requires transmission to be removed to get access to it. RMS is a common source of oil leaks in 996 & 997 and I am assuming that RMS may be leaking in your car.
An oil change for $158 does not sound bad, as long as you get quality filter (Wix, Mahle or Mann) and quality oil (typically Porsche A40 approved) in your engine.
There is a lot information on oils and filters on this and other forums (Rennlist, Renntech). Search is your best friend.
Happy motoring
=L=