Bosch Temp Gauge fitting issues for Invader

[bfish]

The OEM temperature gauge on my '79 Invader 440 no longer works. I was recommended a Sunpro as a replacement but I'm told the model that fits are no longer made, so I bought a Bosch 8217. The gauge fits the dash but when the retaining nut is secure in the block, there is play in the probe tube so there is no seal. Shouldn't it fit tight? The metric adaptors don't fit. So, I'm wondering if anyone has some suggestions on how to get this to seal. Thanx in advance.

[bfish]

Update for anyone making this switch in the future.

The probe on the Bosch gauge is shorter than the OEM which is why the probe would not seat properly. I couldn't find an adapter to fit so the coolant manifold was taken to a local machine shop. The shop ground down the opening of the gauge probe opening and re-threaded the opening till the probe was snug. The probe fits and everything seals up nicely, so I'm ready to move on to the next project.

[Interceptor398]

Very useful information.