Cummins 5.9L diesel owners, listen up! If you've got an oil leak at the back of the engine, it might be the rear main seal. This is a genuine Cummins OEM rear main crankshaft oil seal kit, part number 3925529 (also interchanges with 3934486). It's brand new in its packaging and is designed for the 5.9L Cummins engines, both the 12-valve and 24-valve models. The seal has a metal outer casing. This is a critical seal that keeps oil in the engine and prevents leaks onto your transmission or driveway. Replacing it is a big job (usually requires pulling the transmission), so it's for experienced mechanics or shops. Don't let a leaky seal cause bigger problems. If you're doing a clutch job or major engine work, it's the perfect time to replace this. Keep your Cummins running tight and leak-free!