Yes the pinhole leak was not a manufacture thing, it was almost like a dry rot spot on the cap. These are two seasons
I had a slider one of my calipers seize coming home from fishing last week which got me looking at the hubs. Both rubber caps on the rear axle where dry rotted and cracked. Never seen this before. Fortunately, I had just the slightest bit of moisture right under the cap on one of the hubs. Picked up new rubber caps on the way home this morning.
When lubing the hubs, rotate the wheel while filling and only fill to the end of the spindle to allow for expansion when the hubs get warm.
Hub temps are a combination of bearing friction (preload and endplay among other things), loading, tire inflation, brake activity, etc. Far to many variables to say if temperature X is "good" at any specific time or condition. Therefore I look (feel) for temperature changes over time and differences from side to side. A hub running at X degrees is no better or worst than one running at X+30 degrees as long as the temp stay fairly consistent from one outing to the next.
I'm running grease with a 540 degree drop and a 300 degree operating temperature. At 300 degrees, my hand would blister upon contact with the hub. If you can hold my hand on the hub for 5 seconds or so, I'm good to go.
I used nothing but marine grease for years until I started buying hi-temp lithium complex grease by the case for use around the farm. The equipment get abused 3 times more than the boat trailer so I gave it a try. I've not had any issues.
Technically, marine grease is the better product for the application (better washout resistance) but my "farm" grease has proven to be a worthy substitute given the situation. Then again, I'm pretty anal about seals and bearings in general. Your mileage may vary..lol