That is a really nice looking Transitional. Case looks really sharp and clean. Dial has a little issue with the sub-registers but minimal paint degradation. Also, looks like there has been a little bit of gasket melt on the dial but hard to tell full extent. Hands may have been relumed (I could certainly be wrong on that but from photo lume on hands is lighter than indices' plots).
There are a few other Transitionals I've seen for sale recently around 17000-18,000 euros (vintageheuer.com & Abel is selling his) but Christie's auctioned a nice Transitional last fall that realized price of 13750 CHF or 13400 euros--I feel dial was a little nicer condition than yours but doesn't look like it had box or papers.
https://onlineonly.christies.com/s/...-edit/heuer-steel-monaco-ref-1133b-231/134013
I will defer on what I think is an adequate price. It really boils down to how quickly you want to sell it.
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