If you want to do maintenance on your own car I strongly suggest buying a workshop manual. They're fairly cheap, available from most bookshops and car parts stores and will tell you all this kind of information. VW beetle transaxles do not have a dipstick, so you will need to jack the car up at both ends and make sure that it is still level, so that the level will be right. As you can do this with the wheels on, you could use ramps or wooden blocks under each wheel. Under the back of the car, you will need to unscrew the transmission filler plug and physically check the oil level. I believe the oil should be filled all the way up to the bottom of the filler/sight plug, but check this yourself in the manual.
17mm allen wrench will remove the top fill port. Fluid should be up to the fill port. 3 quarts of straight 90 weight for IRS if I remember correctly.
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