105 8 Speed shifter-Repair or replace

[Slave]

Have a Shimano 105 Shifter (8 speed) on a bike donated for underprivilaged riders. The shifter will change the gears one way but not the other.

 

I took it apart last evening (only as far as removal of barrel from casing.) The grease was very "gummy" and lots of dirt, so I cleaned it with toothbrush and Handy Andy. Used light machine oil to re-oil all sorts of levers and springs.

 

I got the shifter working  again but noted that as soon as I put it back in the houseing, the problem returned. So, the assumption is that one of the springs or levers is worn and the housing limits the amount of lever travel required to change the barrel position and therefore the gear.

 

Lacking the tools to take it apart furhter and reading a thread previously, I also lack the number of hands to do do this.

 

Question is, is the thing worth repairing or should it be replaced.

 

I am sure there are a number of people who have similar problems with Shifters.