The Tartan 27' is an excellent boat, but they are showing their age now. A few things to look out for in the Tartan:
1. Gate valves should be replaced with ball valve (or something similar)
2. encapsulated chainplates (they may be rusty and a bear to get at!)
3. Leaky ports
Other than that, be mindful of the usual things that tend to plague the older boats out there, wet decks, aging engines, electronics,hoses, sail inventory, etc...
Sparkman & Stephens knew what they were doing and these are wonderful little boats. Good luck with your search!