Remove RNAse from pipettes?
According to the Gilson Pipettman User Guide you can autoclave the following parts: Tip ejector, Tip holder and the connecting nut (have a look into the PDF linked above if you are not sure about the parts). All other parts can not be autoclaved. Gilson says the following conditions can be used (page 17 in the user guide): Autoclave for 20 minutes at 121°C, 0.1 MPa.

However, when you really have a DNAse contamination, you will not get rid of it with autoclaving, since RNAses are too stable. You can either try the various solutions on the market which made for killing RNAses or simply get a new set of pipettes used only for RNA work (on a different bench in a different lab with a completely different and fresh set of chemicals and plastic ware). And I would recommend filter tips for this work. They are more expensive but in the long run it will save money since you don't have to repeat experiments.

Regarding your leaking pipettes: The pipettes contain rubber rings and teflon seals in the inside which have to be replaced from time to time. The image below shows how (parts C and D), the ring can be purchased from Gilson. If you don't know how to do this work (and have no technician who does) you can also send in the pipettes for service. This costs a bit of money, but is ways better than to use unreliable, leaky pipettes. 



And don't worry, Gilson pipettes are pretty good. I have used now more or less all brands on the market and I still prefer them. They only need some service from time to time.