Support for Neg. Butvar is pretty good without.
Carbon only films a more trouble to make or more expensive to purchase.
If the UA is too thick that too will cause trouble because a lot of heat is generated in such electron dense material. Apply and blot about six times by touching the grid against a drop of 'stain' and finish by blotting, well but not blotting off all of the solution. This makes an enormous difference because the plastic coatings are poor conductors of heat and electrons. If they are old bench reagents use fresh ones from a good supplier. If its too thick have you tried a spreading agent such as bacitracin.