So, one thing I've noticed is old cars have heavy doors - and I love it. Now, the back two doors on the XJ8 are heavy where passengers think the car is locked when in fact they're not using enough force.
However, the front doors require little to no effort. Is this normal?

 

Yes it’s normal. Lack of use causes door hinges, door check and the actual door lock mechanism to bind. Purchase a can of spray lubricant made especially for hinges and locks. I wish all door hinges had an actual zerk grease fitting on them.

 

oil or grease