What This Kit Covers
This is a two-piece repair: the PTFE rear main crankshaft seal plus the matched wear sleeve that presses onto the crank flange. Buying the seal alone on a high-mileage ISX is usually a mistake. The old crank surface has a groove worn into it, and a new seal riding in that groove will weep again within a few thousand miles.
Position is rear, between the block and the flywheel housing. The seal is a lip-style PTFE design, run dry on install — no oil, no grease on the sealing lip or the sleeve OD unless the service procedure you're following calls for it. PTFE lips take a set from the sleeve and will not seat correctly if contaminated during installation.
Cummins listed this seal and sleeve arrangement across the ISX family, including ISX12, ISX15, QSX15 and the later X15. Physical bore size and crank flange diameter are what matter here, not the marketing name on the valve cover. Confirm against the number on the old seal or your engine serial number before you order.
Why These Numbers Cross
4962603, 3680095, 4101422 and 4926527 are Cummins numbers that appear on this same rear main sealing position across the ISX production run. Some are supersessions — Cummins revised the seal material and the sleeve, and the number changed while the bore and crank flange dimensions did not. Others are the seal-only versus seal-and-sleeve kit packaging of the same components.
PAI 136131 is an aftermarket catalog number for the same rear main assembly. PAI builds its own listing structure, so the number looks nothing like the Cummins ones, but it points at the same bore diameter, the same lip design and the same sleeve press fit. These numbers are printed here for identification only.
Because supersessions ran forward and backward across the ISX line, the number stamped on the part you pull may not match the number in your parts book. That's normal. Match the physical part: seal OD, sleeve ID, and lip orientation. If any of those differ, the cross doesn't apply to your engine regardless of what the catalog says.
Checks Before You Order
Get your engine serial number off the dataplate or the block pad and verify against it. ISX and X15 blocks went through revisions and the rear seal carrier is not identical across every build. VIN or the number on the old part is the only reliable confirmation — a cross-reference list is a starting point, not a fitment guarantee.
While the transmission is out, inspect the crank flange for scoring and check the flywheel housing bore for out-of-round. Also look at your crankcase breather system. A plugged breather builds crankcase pressure and pushes oil past a brand-new rear main, which is why some shops replace this seal twice before finding the real fault.
4965569 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 4965569. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| Cummins | 4962603, 3680095, 4101422, 4926527 |
| PAI | 136131 |
Frequently asked questions
Do I have to install the wear sleeve, or can I reuse the crank surface?
If the crank flange shows a visible wear groove, install the sleeve. A new PTFE lip will not bridge that groove and the leak comes back. On a low-hour engine with a clean, unmarked flange, some techs run seal-only, but the kit is priced and packaged as a complete repair for a reason.
Will 4965569 fit my QSX15 if my book lists 3680095?
Those numbers cross on the same rear main position, and 3680095 is one of the Cummins numbers in this interchange group. That said, we don't promise fitment from a number alone. Verify with your engine serial number, or measure the old seal OD and sleeve ID before ordering.
Why did my new rear main seal start leaking again?
Three common causes: crankcase pressure from a plugged or failed breather, a lubricated PTFE lip that never seated, or a scored crank flange that was reused without a sleeve. Check breather function first — it's the cheapest to rule out and the most frequently missed.
Not sure it fits? We check before you pay.
Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
More cross-reference guides
Need the part, not just the reading?
Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.