Conversation so far:
What did Denny Hulme do after leaving F1?
After leaving F1, Denny Hulme led the GPDA (Grand Prix Drivers' Association) for a brief period.
Why did Denny Hulme only lead the GPDA for a brief period?
The cut and thrust nature of the post was ill-suited to Denny Hulme's gentlemanly nature and he did not fill the post for very long.
What did Denny Hulme do after leaving the GPDA?
Denny Hulme retired to New Zealand, returning to touring cars to race occasionally in the Benson & Hedges 500 race at Pukekohe Park Raceway in the late 1970s

Question: What year did he start to race regularly again after leaving F1?
Self-contained rewrite: What year did Denny Hulme start to race regulargly again after leaving F1?