More likely, the actual leakage is from the stem on the isolation valve. That leakage runs down the valve body and appears to come from the hole bleed valve.

Not sure what an "isolation valve" is. Here is a photo I meant to include in thr original post:

The bleed valve is directly under the red faucet on the left.

Actually, I went to Home Depot today to see if they had a valve cap without the bleed hole in it that would fit. They didn't. But I managed to get some O-rings that fit inside the cap once I cut them down a little. I stuffed one in there, tightened up the cap, and the leak has stopped. So apparently it was coming from the bleed valve and not the isolation valve. Thanks for all your help.

Great! Thanks for the feedback. BTW, the rplacement bleeder caps I buy come with an O-ring in the bag.

PS Are you a Cop in The District? My Nephew is also.

Oh, that's good to know that the O-ring is supposed to be there in the first place. I wasn't sure and the Home Depot guy was clueless. Besides continuously trying to get closer than six feet from me, he was stumped as to either cause or remedy.

And yes, I am a cop in DC, the Fifth District. Any idea of your nephew's assignment?

And is he MPDC? Metro Transit? Park Police? Capital Police? There are quite a few depts in DC.

MPDC No idea of assignment. Was in Narcotics and later Vice. My brother said he was so glad when his son got out of drugs and into vice. LOL

I'm out in th MD suburbs... MC.

Well, next time you talk to him ask him if he knows Ofc. Salsburg, Odds are slim but what the hell. Thx again, buddy.

Side Bleeder Caps

If the above doesn't have the hole, try:

WITH HOLE

If not, Home Depot had them next to the Brass Valves says a couple of posters elsewhere.