Compression test - One cyclinder very low

[Scratcher]

Gents, a driving buddy just did a compression test of his 34 Sedan (sealed 1250) and got the following figures  155 - 155 - 80 - 155. Obviously he has an issue with No3 cylinder however based on the cars performance on the track, no-one would have guessed he had an issue with one cylinder until we did the test, Any advice as to what could be the issue?

[snapper]

Perhaps the valve lash is out of spec on cyl #3.

[knoxracing]

Do a leak down test, this will help determine the issue.