I need to find 2 logs in successive order. One containing "Y", and the last one before it containing "X"

I have a general "error: Y" log, without any unique identifiers, other than the sourceHost and sourceName. I want to find the last message from that source with "Starting job for: X" that occurred before the error. There may be some messages in between the "starting" and "error" messages. I have several hundred to parse, so using the surrounding messages feature is not practical. Most "starting job for: X" result in a "completed job for: X", but some error and the job identifier is not listed in the error