Thanks for all the great suggestions: PROJECT SUCCESSFUL!
I did not need any special cleaning as the torch burned off the oil during the braze (gold in color, almost in the middle of the photo on the rear line. The cylinder was pulled out over a foot, retracting the internals: so nothing near them got warm.
I thought you might be interested in more details of the repair:
I was dredging under a 16' wide, low bridge, so the backhoe had to go all the way under to reach the middle. No matter where I was working, I had problems with striking the bucket hose fittings on my LB1914 hoe on the underside beams of the bridge, soon irreparably damaging the fitting thread and a hose thread
As well as replacing the fitting (changed from JIC to American Pipe) , my talented friend devised and added two guards to prevent a repetition. See photo.
The first guard was made of angle, cut and ground to the right size and shape to fit on the upper edge of the frame of the hoe through which the piston retaining pin goes. It turned out to be not quite tall enough, so a piece of rod was welded on top of it - seen at the top of the photo.
The second guard was designed to protect the line that runs down the top of the cylinder to the bucket end of the cylinder (to the left). It was made from about 4" of pipe (which just fitted around the cylinder sleeve) cut in half; the two resulting pieces had about 18" of strap welded to them on their outside in the middle. This assembly was slipped snugly onto the cylinder from the side, and tapped with a hammer until the strap was upright. It was held in position by a couple of large hose clamps.
You can see enough of the setup to the left of the photo to get the idea, I think. Everything added is black & unpainted. I think these guards are a real enhancement for anyone with exposed fittings who has to work under a structure for any length of time. The limited angles the hoe can work at, the lack of visibility, and especially the difficulty of making slow, horizontal boom swings made damage almost inevitable, and I hit the bridge many times with the boom.
Charlie