Hi Gregory,
Unfortunately I couldn't do a syntax check as you are able to do on SP08, but my replication is working fine with the code that I had pasted.
I see one slight change in the way you have written the code-
Can you try with giving spaces around equal sign(=)
meaning -
IF <WA_S_ZCOIL_EVENT>-MANDT = '100'. <WA_R_ZCOIL_EVENT>-MANDT = '999'. ENDIF.
In order to recreate your scenario, I tried removing spaces between the equal sign and even I too started getting syntax errors.
But after keeping spaces, my replication went fine.
Please let us know if you still get issues.
Regards,
Saritha K