I don't know if it's a actual design issue but that's exactly where both mine cracked. I guess if it helps I ran mine for six or seven years with at LEAST one cracked and other than the stumble you're describing and slight decrease in gas milliage it ran. Noisy, but it ran.:-)

The dealership and a couple other people I've talked to say that our exhaust manifolds don't respond well to being dunked and having cold water splashed on them when they're hot. Guys at the shop say they replace several a year on just street driven vehicles.

Edward

'97 Montero Sport LS 5-Speed 3.5L conversion
SAS Dana 44s & ARBs, 35" Yoko Geolandar M/Ts
NP231 B4R doubler/Terra Low231/RP 5.38 229:1
'99 Montero Sport Limited 4WD SAS 3-link project
'03 Montero Sport Limited AWD
'97 Montero Sport LS 5-Speed 4WD