car will not start sometimes, why? Seems related to how it senses it is in park or neutral.

I take it you mean it wont crank/start, sounds like your starter safety neutral switch is acting up, next time put your car in neutral and try to start it.

I was told it was the transmission cable which apparently a real pain and expensive to replace. Car also uses lots of oil but I see no leaks or burning. Will an additive help the oil and is there a cheap trick to the starting problem?

Here you go big guy.parts store say to the guy neutral safety switch.