2006 Mini Cooper with clutch slip issues- clutch replaced 10-15k miles ago

The clutch was replaced about 10-15k miles ago with a LUK kit (clutch, pressure plate, throw-out bearing) and a new flywheel. We didn’t replace the rear main seal at that time.

Symptoms:
• Clutch engages high.
• Slipping in all gears — e.g. In 2nd gear, pressing the gas causes the engine to rev without increasing speed.

- Has anyone seen clutch to wear out this quickly?
- Could a leaking rear main seal cause oil to contaminate the clutch and lead to slipping?
- What else should I check? Could it be a faulty slave cylinder, clutch adjustment issue, or something with the flywheel?

Any insights or thoughts would be really helpful. Thanks!