Sorry for the amateur question, /o/, but I've had this 280SE W116 for about 3 months now, and I can't seem to figure out what this container is. The car has hydraulic suspension, so my dad thinks that hydraulic fluid or something might be kept in it, but we're still unsure. I can't find any information on it, nor can I find any other 280SE models with the same container. Any help would be appreciated, /o/.

Pics related, container in question is outlined.