Seal -- Locking Down $6 Million Bachelor Pad

A CHANGE IS GONNA COME for Seal ... at least in terms of where he lives ... 'cause TMZ has learned Heidi Klum's estranged hubby made a formal offer on his very own bachelor pad in L.A.

Our real estate sources tell us ... Seal has been eyeing a 5,500-square-foot mansion in Brentwood recently -- which hit the market 18 days ago for $6 MILLION.

We're told Seal perused the place all week -- and then formally made an offer on the 4-bedroom, 5.5-bath abode after his 3rd visit.

The crib is a panty dropper to say the least -- it's three levels ... runs on green energy ... has floor-to-ceiling windows ... a fireplace in the master B ... a media room ... gym ... and TWO separate kitchens.

Ya know, for entertaining more than one lady at a time. Niiiiiiiice.