One of my kids requires syringe feeding.  I tried a number of things to
extend the life of the syringe.  I found that oils, etc. (ferretone, olive
oil, etc) tend to destroy the rubber (noticed first as black residue left
in the tube).  What works best for me, and allows me to use a syringe
several months, is simply dipping the plunger (rubber part) into the food
before attempting to load the syringe.  I just coat the end pretty well -
and it slides nicely.  It's a tad bit messy at first until you get the hang
of it - but I've been using this method for 3 years with good results.
 
I also use a good quality syringe to start with.  I like the "Comfees"
brand oral syringes - intended for administering medicine to children.
 
Hope this helps.
 
Cheryl and the Wrecking Crew
[Posted in FML issue 2458]