Growing up, we had some classic cars around. But living where we did, dust and extreme heat were the enemy of what nearly every car had: a whole bunch of vinyl. Coated with dirt and left in the hot sun, the vinyl, especially on exposed dashboards and seats, would crack and need to be replaced. But there's a simple maintenance trick you can do to prevent that from happening!
The reason vinyl cracks so easily under heat and dust is that it doesn't retain moisture well. Unlike leather, which can absorb a little moisture to keep it supple, vinyl has trouble maintaining that flexibility, and instead of bending under stress, it cracks. So what we have to do is give it a way to hold on to moisture and allow a little flexibility.
First, clean it with mild soap and water. We don't want to trap dirt in any cracks: that'll only expand them more quickly! Then, get a microfiber cloth, and drip a small amount of baby oil directly on the rag. You won't need much! Rub the oil into the vinyl in small, curcular motions. You can add more oil to the cloth as you go, but be careful not to overdo it, or the vinyl will become greasy.
Your vinyl will look great, and better withstand the elements!