Tsunami / Sceptre topside to liner joint ?

[abl1111]

Just noticed something that I need to repair on my 1975 23' Tsunami and hope I can get some advice from somewhere who has 'been there'.

At the helm, and the passenger side too, there is a topside to liner joint, that runs horizontal, directly under the foot rests - it's hidden behind some teak. This joint is about 1/2" to 3/4 " wide and filled with Potter Putty. Mine is cracked on the passenger side, along the whole horizontal bottom ( the vertical side part seems still intact )

I want to grind this out and re-bed. My questions:

- How deep do I have to grind this ? I don't want to grind too far. Do I grind from the just outside, or inside the cabin too ?

- What would you recommend I fill it with ? I have a lot of resin - can I mix this with cabosil and use that, or is this a good place for epoxy ?

Any advice appreciated. BTW - how I found this was I noticed a little extra movement in the teak door and the door jamb, while closed and under way. I knew something was 'not right'…