Couldn't find the TSB but it appears after the smallblock chev appeared in 1955, the exhaust manifolds got pretty close to the steering gear. The heat thinned the gear oil and leaky seals in the box ensued.
Follow this thread it is interesting.

https://www.trifive.com/forums/archive/index.php/t-122622.html


1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration