Source of crude painting in good health (3,4)
I believe the answer is:
oil well
'source of crude' is the definition.
(I've seen this before)
'painting in good health' is the wordplay.
'painting' becomes 'oil' (oil painting is a kind of painting).
'in good health' becomes 'well' (similar in meaning).
'oil'+'well'='OIL-WELL'
(Other definitions for oil well that I've seen before include "Will Leo? (anag.)" , "What extracts riches" , "as result of a strike" , "How to avoid friction" , "source of serious income" .)