I've experienced the same problems with the small BW tranny as well. I had one behind a relatively stock 304 in a '70 Javelin. It is just way too small for a V8 application. I had mine in the tranny shop quite often until I went to the 401/998 combo I have now. The small BW has tiny clutches and the tubes have a habit of leaking. I even had to replace the case because it cracked in several places! I found a replacement from a Postal Jeep! It's just too light-duty for a V8. If you really baby it, it should last you for a while.
Bill Dettman
'74 Matador X 401, '70 Javelin 401 BBG
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