Hello Martin,
Yes the piston cups and seals are likely worn and would be needing a rebuild kit. The rebuilt kits for the Brookwood Vertex Compressors can be ordered here:
http://www.thepondreport.com/store/repair-parts-brookwood-compressors
If your pump is 8 years old make sure to check the model number as the pumps have been updated since you first purchased the pump and it may require an older model repair kit.
If you need help the best way to contact us is by email especially during the holiday season. Our email is info@thepondreport.com
Samantha