The MTC monovalve cores are so cheap and easy to replace (unless you have buried it during your conversion) I suggest just trying one to see if it cures your problem. If it does, buy a couple of spares and change as needed. That was my approach.

As an alternative, for a reasonable price, KLIMA offers a monovalve elimination kit that promises a different method of heat control. Check it out at:

https://klimakit.com/product/monovalve-and-coolant-circulator-pump-eliminator-upgrade-kit/