B757 Captain experiences leading edge slat disagree on departure and diverts to airport with longer runway. After maintenance action; flight is dispatched to original destination where problem reoccurs during approach but disappears prior to landing.

Narrative

Normal noise abatement takeoff with flaps 15. On flaps retract got 'LE SLAT DISAGREE' EICAS and leading edge light illuminated. Flap indicator showed flaps between 0 and 1 and flap handle set to up. Held 200 KTS airspeed; First Officer flying; advised ATC would like to restrict airspeed and climb to work problem. Cleared to 13;000 FT with vector and performed irregular procedure LE SLAT DISAGREE; contacted dispatch and maintenance. Maintenance advised unable any help and we advised dispatch and ATC divert to ZZZ. Leading edge light remained illuminated after irregular procedure LE SLAT DISAGREE; then performed irregular procedure LE SLAT ASYM. Declared emergency with ATC. Cleared visual approach ZZZ. Checked landing distance table. Autopilot disengaged and performed controllability check. Approach and landing with LE Slats up; flaps 20 and Vref30+30. Advised ATC on landing no further assistance required. Maintenance worked on aircraft 2.5 hours and found one right wing LE Slat load sensor tripped. Reset; checked flaps operation five times to full up/down travel. Released aircraft; added fuel; re-dispatched to ZZZ1. On right down wind with flap extension to 1 got all same indications as stated above. Advised ATC emergency. Extended down wind for approximately 10 miles. Performed ALL actions as stated above. Advised dispatch via ACARS emergency. On final LE SLAT DISAGREE EICAS and Light extinguished. Slats/Flaps extended to 20 via alternate switches. Ended Irregular procedure and normal airspeed landing flaps 20 and slats extended. Advised ATC landing no further assistance. Taxied to gate and left flaps/slats extended for maintenance. Maintenance advised need to replace LE Slat Load sensor.