I have one of these funnels that works great for filling the ZF.
Right Angle Funnel
https://www.beemershop.com/pro.../redline-funnel.html
Other similar options are readily available, or even a tranmission funnel with a flexible tube.
Generic angled Funnel
https://www.amazon.com/Plastic...illing/dp/B0BMPBMT68
Transmission Funnel
https://www.amazon.com/Funnels...ission/dp/B0B5MHPDQV
I used Castrol 90 wt Hypoy Gear Oil if I recall correctly. Be sure to let the bottles rest in a bucket of HOT water for a bit so the oil flows a little easier. Allow the oil plenty of time to slowly ooze through the internal passages of the ZF to the other cavities.
Also, the 17mm VW oil plug sockets are readily available at your local O'Reilly Auto Parts, or Autozone. Or, from a number of online sources.