Do I need to download it again???

[JoeyBaloney]

So you know how you can have different accounts on Macs? Well I signed into Steam and downloaded Gmod on my brothers Mac account. Now when I try to play it on my account, it acts like I need to install it again. Is there any way around this?

[All0utWar]

It will probably just install a very small patch.

[sporeguy]

It probrbly is just updating