[davepnw]

I think your approach was correct to a point. Probably that box already had damage from being run without lube.

When I say correct to a point I think you have to make sure it's packed pretty full, and keep trying to get more grease in and the air out after installation. So here's what I'd do on the next box you install.

Use a thin chassis grease, that will let it work in easier. I'd try to lube it the best you can before you ever put it in the car with the tube you used previously. If you can find a spot to drill and tap another pipe port that would be great. Use it for a vent. Then drill and tap the fill plug for a grease fitting. Work the box through its full travel several times, adding grease if it will take it. After you've installed it, put a few shots of grease it in once a month until it won't take any more without pushing it past the seals or the vent (if you put one in). After that it shouldn't require attention but once every year or two.

I did the same thing years ago, one of the bolts on the top that are tapped all the way through can be removed to serve as a vent while filling, then reinstalled. I made up another filler plug and drilled/tapped a grease fitting into it, afterwards I removed it and reinstall the original plug for the stock look. Dave