As a final up date! Thanks again for all remark..
Removed all parts [wheel/drum etc] :the entire unit including inside of rear wheel were saturated with brake fluid;no wonder reservoir was near empty.
Cleaned all down..removed all traces [? ] of brake fluid.checked the movement of cylinder pistons and shoes.All seemed ok..no leaks.Cleaned re assembled..tested..taken on `safe` road..emergency stops [in reverse also].Stripped again..no sign of fluid..stood with brakes full on for a couple of hours..nothing??
another one of lifes mysteries?? better replace the cylinder ??