Investigating an Oracle 12c outage after the fact, while limited to SQL*Plus Warning up front: unfortunately I'm limited to using SQL*Plus on remote site, with no other tools available. This is Oracle 12c (12.2.0.1.0) Standard Edition running on Windows Server 2012R2. 

Over the weekend there was an outage where Oracle stopped responding for approx 15 minutes. Looking at application logs and Oracle's alert log, it was clear that something tied up Oracle until it hit an ORA-04031 e.g.

ORA-04031: unable to allocate 64 bytes of shared memory ("shared pool","unknown object","KGLH0^b3e62c9b","kkocsBeElem: kkoMergeBindEqvCtx")


My problem is that I don't know the cause of this issue. My question is, what tools are available to me at this stage 48 hours later, to figure out what happened? As mentioned I've been through the alert log, and the application logs.
You can inspect V$SQL for statements that don't use binds, eg.

select substr(sql_text,1,80), count(*)
   from v$sql 
   group by substr(sql_text,1,80)
   order by count(*) desc


Then inspect the full text of the statements that come on top, see where they differ.