The 1000 Bar pressure is well within the limit , so this may not a reason for your case.
Water and ACN are also used extensively in HPLC , if in doubt normally fine filtering change of supplier or vendor are the few of the things that we do to isolate this type of trouble
Also TFA you are using , is there a possibility of using some other stabilizer , or using TFA at a lower concentration are few of the possibilities that can be tried.
Please note there are no frequent plunger seal failure notice or defect on this part has been observed , we suggest you to try our suggestions .
If you need more information or if the problem persists, please call 1-800-227-9770 and choose option #3 for Technical Support.
Agilent Customer Support
Thank you Agilent Customer Support for providing this response.