Dawn Wells — famously known for playing Mary Ann Summers on the iconic TV show, “Gilligan’s Island” — is now sadly suffering from dementia and needs some court help with an overzealous fan … according to new legal docs.

Dawn’s manager, Leonard Carter, filed legal docs on his client’s behalf claiming a man out of Ohio has been harassing the 81-year-old actress with phone calls and letters since March and is trying to take advantage of his celebrity client, who he says suffers from dementia … this according to legal docs obtained by 360aproko.

In docs, Carter claims Frank Bennett has caused Dawn “great mental angst” because he’s an “artful manipulator extracting Dawn’s personal info” … like her SSN. Carter claims Bennett’s a married man who has professed his love and desire to marry Dawn. Carter insists Dawn’s rejected Bennett’s advances, but says he won’t stop contacting her.

What’s more … Carter says a handful of employees at the assisted living facility where she resides have witnessed Bennett’s intensity. Carter claims Bennett’s “unstable and could snap and do physical harm.” He also claims Bennett told him, “If I am visited by one cop, if I am served with papers, It’s game on!”

The judge granted some protection for Dawn … barring Bennett from coming within 100 yards of her.