This just happened to me about 500 miles after my last valve adjustment. I was doing 60 when it stopped making power. It was still running but as you can imagine it was tapping loudly. My intake valve and adjuster got mashed.
You can see where the valve stem is smashed by comparing them.
Here is the bad intake vavle
Here is the good exhaust valve
Smashe intake valve adjuster is on the left
Had the dreaded base gasket leak too so I pulled the cylinder and also found my oil ring was stuck.
Been with out my TW for TWO weeks waiting for the parts. Being T-Dubless is excruciating!!!