Don't know about the vinyl protectant but for cleaning I use a brand called "awesome". You can only buy it at the dollar store. Very strong cleaner so dillute it a bit with water, but makes seats shine like new and takes stains out of carpet. Good stuff!
My wife and I have been using vinyl cleaner for years and it doesn't really help with mold and mildew. We discovered a new product called Krud Kutter that seems to get at the little critters. She applies Krud Kutter, lets it soak in, then gently rubs the vinyl with "Magic Eraser". That's the cleaning part. When she's done she rubs the vinyl cleaner on with a damp rag. The seat cushions look like they did in the showroom. Sorry it took us 20 years to figure this out.
BTW, Krud Kutter is also good on canvas. You can visit my blog for more information.