In reply to a PM:
Your SSEi has a paper gasket between the SC and LIM. It also has two yellow coolant o-rings. Your LIM has 4 gaskets between it, the block, and the heads.
The most likely leaks are at the TB gasket or the LIM gaskets. But with those miles, you should just replace them all. I can do the whole top end in about 2.5 hours on an L67 or L36, so even for a first-timer, it'* a one-day job. You should replace the black plastic coolant fitting on the waterpump end of the LIM with a replacement metal fitting from the dealer while you're at it.