The piston seals for your Agilent 1100 are made of polyethylene blend (resistant to almost all HPLC solvents) and run well for hexane/Propanol using isocratic or gradient mode. When you use very strong organic solvents like pure methylene cloride and toluene you can reduce life of your seals. Also, there are a "few" solvents for which Teflon seals are more suitable.
Depending on HPLC use, you could change your piston seals every 4-6 months to minimize
Suggestion: Read your Operator Manual of your Agilent 1100, normally you find information about what DO or DON'T with your HPLC system