Also, which head gasket are you using?
Also, which head studs are installed in the block? The original A-prefix, low-spec studs (A907E0224ZD), or the later B-prefix, high-spec studs(B907E0224Z) .
Which torque spec are you using on the nuts when installing the head?
The manual for your 1985 Turbo Esprit would have the original low torque spec that was intended for the A-prefix 'weak' studs.
70 lbs-ft ( 9.7 kgf-m) Front & Rear Pairs.
75 lbs-ft (10.4 kgf-m) Three Middle Pairs.
Oiled threads & washers.
That's too low for the current composite head gasket.
When the composite gasket was introduced in Jan 1993, it was a package deal that included new, upgraded head studs plus a new torque spec & procedure. When installing a composite head gasket in an older (pre-'93) engine, you should have also replaced the studs with either the B-prefix studs or the aftermarket ARP studs.
Instead of a torque wrench, the new spec called for the use of a Torque Angle Meter (TAM). The new torque spec was:
Cylinder head (tighten cold, oiled threads & washers):
i) 20 Nm (initial pre-load via a torque wrench)
ii) + 75 Degrees
iii) + 40 Degrees
iv) Wait 5 minutes minimum (longer is better)
v) + 20 Degrees
That's not only a different method, it also produces a significantly higher clamp load.
ARP requires the application of their own proprietary lubricant on the threads and washer prior to torquing the nuts. Their lube spec has changed several times, and the torque spec has changed with each lube formula. So follow the torque instructions that come with the ARP lube you have. The ARP studs are all the same, the torque changes with the lube. Currently, the torque is
ARP Studs & Nuts with Lotus’ 1993-onward Goetze Composite Head Gasket
110 lbs-ft (15.2 kgf-m) All Studs, ARP Ultra Torque Lube applied to threads & washer.
Besides the higher torque, the ARP studs & nuts also use a fine pitch thread (a narrower 'wedge' angle). The result is a significantly higher 'clamp load' on the head. However, I fear that ARP's torque spec is right for their own product (the studs) without having any specific knowledge of the engine you're putting them into. It's the same old aluminum threads in the 9XX cylinder block that's hanging onto those new ARP studs, and resisting all that higher torque & clamp load. I've recently heard from a shop in Colorado that installed ARP studs in a customer's Jensen-Healey's 907. The ARP torque pulled one of the studs right out of the block. I'm not saying don't use ARP studs... just that I wish I knew more about the specifics.
So... have you been using the original studs and torque for your '85? Or later studs and higher torque? With the old studs & torque, you aren't taking advantage of the composite gasket's capability.