Thanks for the replies.
We noticed a depression in the bottom of the groove. When we felt around it with a pick, we couldn't feel a hole for a drain back port. I guess the next step will be to remove the dust shield and take a closer look.
The blow-by is an interesting thought. The tractor burns a fair amount of oil and was already getting a new set of rings while it is in the shop this winter. The leakage could very well be related.