Well, if it is all coming from below- you may be right. Engine model numbers etc could be helpful.

It is a B&S Vanguard 20hp model 358777 0280e1, purchased new in 2005. I had my tech take it to his shop as this is beyond my capabilities, but have not heard from him. The big downside is that I now have to cut my 1 acre lawn with a 20 inch Honda, should take me the better part of the day!

Will be a good idea to replace the seal but I think you may find out that the sump cover gasket has broken.
Briggs Vanguards (and some other B&S) have had issues with that.
There have been a few discussions on here about that exact issue and some fixes to help keep it from being a "chronic recurrence".
Make certain that only genuine Briggs parts are used and there is an O-ring oil pressure seal that should be replaced also when the sump cover is removed.

I will call tomorrow and find out what is going on and repost. The oil spatter was on the lower frame, nothing around the oil filter or anywhere above the motor mount which is why I suspected the PTO but you are right, could be the sump.

I guess I am in for some $$$ in repair bills, but just glad I noticed it from cleaning the deck each time I mow otherwise I could be into a repower situation which would be much more expensive!

Well I must have missed that you are sure the oil is all appearing below the frame on my first read of this.
If it were in fact a sump cover gasket you would certainly have see oil on top pf the frame too.

PTO gasket / seal were shot.