DOS - Can't swap DOS heads between two DOS units

[reefdiver73]

Are there different "lots" or different manufacturers for the DOS?
I was troubleshooting a problem today and thought "well maybe this DOS head has seen better days"...
I took one off of another DOS and even being careful to line up the little "+" gear I couldn't for the life of me get them to snap interchangeably between the two DOS units.
Has anyone else had this problem? They work great on the DOS they came on... Just can't swap them.
I'm hoping this is an anomaly or something I was still doing wrong because at some point I am going to have to buy new heads just due to wear and tear.

 

[SuncrestReef]

I've never seen any difference between DOS heads or DOS base units. They should all be interchangeable.

Have you inspected the old and new heads side by side?

 

[reefdiver73]

Yes. The heads look identical to me... I just can't get the one to snap in. I'll write it off as being "me" for now. We'll see for sure when I go to replace the heads.