Gearbox issues and Service

Hi there

My Alphard Hybrid 2.4 2006 Camper conversion developed an intermittent gearbox issue on a recent run up to the lake district. After a few long days of driving and a few very steep hills the gearbox would crunch when changing down, usually at low speed in low gears. It did it for a couple of days and hasn't since apart from on one or two occasions.

This is a new thing as it hasn't missed a beat in the 10 months we've own it.

The box does seem a little noisier or maybe I'm just noticing engine noise more now?

The garage that has looked after the van for the last 6-7 years said they wont touch the gearbox.

Is this a common issue?

Has anyone got a recommendation for a specialist who could take a look in the London Essex area? I saw someone recommending Rainham Motors...has anyone used them?

Thanks

Edited 3 hours ago3 hr by Jerry_R
Vehicle details and spelling error!