The secondary measures as 6H in series with 100Ω.

The usual method of measuring leakage inductance doesn't seem too successful: with a shorted turn where the primary goes, the secondary inductance only reduces to 5H.

The CT in question is rated 100A:50mA.

Obviously, I could just model it as L1=1.5uH, L2=6H, K=1, but I'm pretty sure that K≠1