I had the same problem with my GC8, even after a mechanic did them it needed doing again though mine were changed over so dry.
You haven't got a ratty hose that's expanding under pressure have you?

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Beaten up old 98 Gen 2 Liberty, 13.0, stock V3 STI running gear.
07 Transit motor home
69 VF & 70 VG Valiants needing full restoration
Yamaha Zooma 50cc rocket hopefully going with the Transit.