i have a 1972 vw beetle. what motor oil should i use? i would like to use synthetic.?

I use a straight 30W in all my air cooled VW's. Never saw the need for synthetic.

If yours doesn't have a drain plug only the screen plate, get one that has the plug. I drain and refill my VW's every 3000 miles, and only check/clean the screen every 20,000 or so.

You may use synthetic if you want. It certainly is better oil. However, since there is no filter, you still have to change the oil very often. Every 3000 miles. So you will be spending a lot for synthetic that you will be throwing away. If you run it through a centrifugal filter and separate out any water, you can put it back in if you want.

But personally I like Castrol 10w-40 in the winter, and 20w-50 in the summer.

Use a Cheap, Ordinary Motor Oil. THAT's what Those old Beetles grew up On. And that's what They run Best On. :)