Outer Limits 4x4 Board

Hi pretty sure im missing my sealing grommet in the g/box, looked at the workshop manual to where it should be and cant see it on mine. i can see the hole where it should be and can poke a toothpick up in there so guessing i dont have one. i hardly drive the car but need it done before i start doing long camping trips. Is it easy to replace (sikiflex or hammer a grommet in) and roughly how much would it cost (even at a mechanics to do it)?

Any help would be great


89 swb patrol pet manual