A client has attempted to use a borescope to inspect the piston crown On a John Deere engine (the commonly delaminate on head gasket failure)
Inspection was attempted through the inlet manifold which has EGR
The residual carbon is obscuring the scope lens.

Is there a product the someone has found successful in removing this residue on an engine which will still run?

There would be a huge time benefit to being able to diagnose without removing the head, over a days work!