PA-60 pilot reported the nose landing gear failed to retract after takeoff. Ground observers confirmed the gear was extended and pilot returned to land.

Narrative

The airplane was previously in shop for nose gear re-seal (had a small oil leak). This was the first flight after the repair. The plane was preflight with extra attention to the nose gear area - all appeared OK. After takeoff I noticed the gear up light not illuminated - Checked the nose gear position in the prop spinner as per procedure and saw the nose gear still extended (mains were up) On an IFR flight plan I notified ATC of a possible situation & asked for time to trouble shoot as I got clearance back to ZZZ - The airport was contacted with manager and mechanic on standby to do a visual confirmation of the nose gear more important that it was 'straight' as the reflection in the spinner looked like it was not - After making passes at the airport it was confirmed (as good as you can ) that it looked 'OK' - A normal landing was made and the airplane taxied to shop for inspection - @ this writing the cause of the nose not retracting was still not resolved - In retrospect I can not think of anything that I could have done as pilot to check the operation of the gear pre-flight?