Taking a tension apart to clean it isn't terribly difficult. Don't be afraid to try. Just pay attention to the order you take it apart in. Tools for self reliant living (TSFR) has an excellent guide on repairing old sewing machines. It walks you through rebuilding and adjusting tensions very nicely.
http://www.tfsr.org/pub/technical_in...echanism_2.pdf
I haven't messed with a featherweight so I don't know if there are any quirks to be aware of.
Rodney