The difference between both [l] and [r] is what Korean people most wonder about in English pronunciation because both are heard alike to them. But looks like the difference was clarified when ‘the perfect edition of [r] in English’ was published on Bruce’s internet cafe (http://cafe.daum.net/blakeenglish) in 2009.
Both original sounds are as follows respectively.
[r] [( )]
Both original sounds are written very alike in HMJ phonetics. Also [r]’s original sounds contain [l]’s. So both are heard alike to Korean people.