Optimax Pitot Tube

[Nasher]

I’d like to reinstate the Pitot tube speedo facility on my newly acquired 2003 225 Optimax.

The main tube, Item 11 below, has been cut off inside the tray.
The remains of the tube are hanging out the bottom of the Swivel Pin with connector, item 8, on the end, but it’s corroded and after flushing out and freeing off won’t grip a freshly cut tube end.

I’ve not had the bottom off the leg yet, but am hoping the fitting shown at the bottom of the image is still screwed into the gear casing and is reusable.
I can’t feel a tube end down inside the hole, but obviously it’s a small hole and my finger won’t fit far!

Looking online, to replace all the tube and parts from the sender down is stupidly expensive using Mercury parts.

My plan was to use a single length of tube from the sender right down to the top of the gearcase, with a big enough loop under the cowl to give enough slack when dropping the gearcase off to disconnect the tube at the top of the gearcase.

I have stock of several different Pneumatic pipe sizes at home, but the nearest equivalent is 4mm OD where-as the Mercury tube is 3.7mm OD. The 4mm does fit inside the connector item 8, but again the connector doesn’t grip it.

Does anyone know if the Mercury tube is a standard size?
Imperial maybe?

Or maybe I can use my 4mm OD Tube and find a way to connect it to the sender and gearcase fitting.

I’m assuming somebody on here has already done this, so don’t want to reinvent the wheel.

Thanks

Nasher.