Danno,
On my Orion I had a buzz around the 7th fret the first winter. I took it into a local shop and the luthier reseated 8th fret and gave it a slight filing. This fixed it for all of 20 bucks. Without having seen your bass I'm betting it is something simple like this.  
 
Keith

Good file technique should give perfectly level frets...I'm a jeweller with 15 years experience so I know filing; any GOOD repair guy should be the same...I haven't watched the Plek at work so maybe I'm missing something,
 
.001 mm of accuracy.  I don't doubt that is possible by hand but I imagine it is going to take some serious time to get every fret that even/level with one another with a file.
 
Your mileage may vary but I wanted to share my experience with it.  There aren't enough words to express how big a difference it made and I was fairly skeptical going into it.
 
danno,  sounds like they were trying to get more money out of you.  Bummer.

The bill was 81.28 with tax for labor to scan bass on Plek and establish that frets are too irregular for a grind & polish. The term roller coaster was used to describe their condition. As the bill was being printed, the assistant asked how many did I own, I replied currently 12 but have owned 5 more. Well no wonder they'll take care of it for you.  They also implied that it wasn't made correctly. As I was rolling down 30th on my way back to Jersey.I get a call on the cell. Did I explain our estimate policy? NO. You can apply the labor amount to work done within a 30 day period. No Thanks. We could apply that amount to any other job, would yoube interested in that? No. Well thats your choice.
You never get a second chance to make a first impression. You can guess how impressed I was. New Yawk, just like I pictured it!

Danno - this emphasises that Plek is just a tool - not necessarily the right tool for every job. That's why you should go to a Plek shop run by a good luthier. Or alternatively go to a luthier who is familiar with Plek and is busy enough that he/she will refer you to Plek when its appropriate.
 
The problem is the machine is so expensive it creates a commerical imperative to use it as much as possible.
 
The medical analogy would be say CAT scanners. A good GP will do an initial diagnosis and decide whether a cat scan is needed or not. But walk into a specialist cat clinic and you're always gonna get scanned.