depending on which model and year, the transmission is sealed which is why there is no dipstick. Dealer recommends change every 90-100K miles but if you read the forum notes from Rialta owners, you may wish to change more frequently, every 40K....I changed mine at Aamco and it cost $215 and has national warranty.
The dipstick kit is a waste of time. I took the dipstick out and installed a VW seal cap on the filler tube. Once the tranny is filled the proper way, and sealed, and there are no leaks, there is no need to ever add oil untill the oil is changed. Rialta has a CD out that tell you how to change the oil and filter, yourself. It is very easy and costs about $75.00. All of the VW Eurovan parts can be bought on line at partsgeek.com, at a very low price. The correct oil level is not accurate with a dip stick but is determined by a overflow pipe on the inside of the tranny oil pan. There is a small allen seal screw on the under side of the oil pan that lets oil run out when the proper leval is reached and the oil is hot. That is the proper level and method.