There seem to be two booloader files shipping with 1.04 namely:
// File = Mega2560-prod-firmware-2011-06-29.hex
// Loader start: 3E000, length: 8192
// MD5 sum = 1E 35 14 08 1F 65 7F 8C 96 50 69 9F 19 1E 3D F0
// File = stk500boot_v2_mega2560.hex
// Loader start: 3E000, length: 8192
// MD5 sum = D9 E6 6B 4E D1 A6 11 2C 61 8F 9B D5 5D 24 E2 13
However neither has the MD5 sum of the one that I found to work namely:
// File = stk500boot_v2_mega2560_fixes_watchdog_problem.hex
// Loader start: 3E000, length: 8192
// MD5 sum = 8A F4 7A 29 43 A0 D8 7C DB ED 09 A3 8F 40 24 1E
I would still recommend the "fixed" one from: