At last, found the original tamil song for 'Paa' movie 'Gumm Summ'. Here it is. Composition and Song by Illayaraja for the song Sangathil Paadatha kavithai - Auto raja(1982). Here's the clipping.
See also, a blog post in 'The observer'.
Awesome music by our great legendary musician Isai Nyaani Illayaraja.