what year gtv? if its a 916 model you'll probably prefer a 156, but the 155 silverstone has the better 8V ts engine so id prefer the 155, the silverstone is an early narrow bodied car so look for one with NO rust on the rear archs as they are not availible even second hand. Agood one will be hard to track down as there thin on the ground now.
The 8v engine is a very stong motor just look for a good oil level as a sign of how well its been cared for, timing chains require very little maintence but can work loose and rattle so listen for that.
Rust on the skinnys is common in the corners of the boot floor behind the rear 1/4s.
If your looking for more refinement and a newer example the later widebody cars can be found easier in good condition, and have the more familier 16V ts engines, (worse motors than the early 8v ones IMO)
Basically, a good well cared for example is the way to go and a good service history and enthusiastic owner will be the best buy.
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