What do i need to fill gap and seal eaves to felt roof for outdoor cabin?

[Fender Stratoplaster]

Hello, doing some repairs and painting garden cabin - one side of the cabin gets weathered a lot as takes the brunt of the sun so I've re painted with an oil based paint

Had to take the fascia boards off the eaves as they were cracked and getting a lot of moisture in, have patched and repainted including on the inside of the board which hadn't been done...

When we took then off there was a very thick rubber like strip under the lip attached with a thick yellow amber layer of glue, which was acting as a seal from the water getting to the wood, and sat under the lip, bridinh the gap between the top of the felt roof. The seal had failed so we took it off but I can't foe the life of me find where to get a similar replacement

Attached are pics of the eave and board

Anyone know what product i need to use to match what was there before or have any suggestions on what they use instead?

At the moment I was debating about using the thickest bit of weatherstrip I could find and then covering it with black bitumen sealant or similar

Thanks in advance

 

[catlad]

Flashband could be used to cover the gap.