I have a 2003 TXT PRO 300. It has blue plastics.
As far as I understand how this all worked out is this.
2002 - Pro engine introduced 125, 200, 250, 280
2003 - Pro engine tweeked for reliability and 300 added at some point in the year
2004 - 300 Officially released with silver plastics etc.. and some fanfare.
If I am incorrect, someone will correct it.
OH and if you would like to look at pics of different years
http://gasgasmuseum.com/
seems as though the museum site is currently having difficulties. I am unable to click anything or nivigate on that site.
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