It looks like it's leaking on the dipstick tube bottom o-ring. 1.9 mm thick, 9.8 mm i.d. Amazon.
edit: I would never pay $10 for that o-ring. Try this one.
I have my own 87 tintop I just started, and I hope it turns out this well. I love your good engineering. Spend money where needed, don't when you can make it better than bought.
