It is time for a new rear main seal for my 2001 HO Cummins. It has been dripping a long time and I remember reading a few years ago about alignment issues with the teflon seals allowing even new ones to leak after installation. Some guy was selling rubber ones on ebay at the time claiming that this mitigated the problem. My problem with ebay, or any aftermarket seal source, is that time after time when I buy aftermarket seals, they harden and leak after only 6 months to a year, whereas the original seals can last decades. I am getting tired of wasting the time and labor to change seals that don't last. Wrestling a HD transfer case and NV5600 tranny is not something I want to have to do every 6 months. So here is my question; The OE Cummins teflon seal is known to leak sometimes even when installed correctly and aftermarket seals have hit-and-miss reliability... what seal can I rely on to be a long lasting fix?

 

I never had the Cummins seal leak when installed really correctly. (And with an undamaged crankshaft)

The cheap rubber seals that harden over time are a pain in the back, because you have to wrestle the trans and t-case.

Cummins offers a speedy sleeve for the seals, usually the crank has a groove after the first or second seal has been used up. So IMO you should at least try the speedy sleeve and the correct seal for application with the sleeve. (I did this on some excavator engines, sleeve plus seal life about 5-7 k hours after repair- still dry when the machines were sold)

 

I've installed well over a dozen Cummins rear seals and never had one come back leaking. I've never tried an aftermarket seal in this application because I've never had a reason to doubt the OEM ones.