Sold my 88 GT turbo a few years ago, possibly the most fun car I've ever owned, it was running a t25 with epic amounts of lag at 24psi on stock internals, just rejetted the carb, bigger intercooler and uprated clutch. Head gasket blew the first time i took it out after turning the boost up from 12psi to 18psi, i noticed water would some times randomly spray up the windscreen on the left hand side, turns out the coolant hoses were pressurising under boost and it was spraying out of the expansion tank cap out of the louvered bonnet vent other than that it still drove perfectly, no smoke out of the exhaust or anything but it failed a leak test and had rock hard swollen coolant hoses, i had to top the water up with like 2 litres of water every time i went out.
I waited for the HG to fail epically before i was going to change it, never happened, drove it like that for a good 6 months and even turned the boost up further to 24 psi with the head gasket already blown, Still drove like a champ and i only changed the HG when i came to sell it. Was always paranoid af driving it tho. especially in the summer in the heat. It sounded absoutley epic tho, god i miss that car but not the paranoia, my clothes also used to stink of fuel after taking it out, not sure what that was all about. oh did i mention it was scary af too? 70mph on the motorway felt like 10 thousand miles per hour the smallest cross wind made it feel like the car was about to flip over or lose control, The first week i had it some drunk guy stumbling out of a pub came over while i was at the lights and shouted, my mate had one of them years ago, crashed it and he burned alive in it, light turned green and i drove of thinking well thats not a very encouraging start to ownership