The input shaft of the NP242 is shorter than the NP229. Make sure there is enough shaft engagement on the seal. If not, there are seals you can get that have a "snout" on them that will reach 3/8 or so further back to reach the shorter input.
85 Wagoneer 5.2/44RE/NP229
98 TJ 5.9/46RE/D300
01 F250 Powerstroke
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