the spring is stretched and damaged so needs to be replaced in the first instance, but how did it get like that has it been removed and refitted badly? is the one on the right ok?if so you should be able to match it up quite easily or if you are not mechanically minded contact a repair shop and they may be able to post one out to you off an harvested machine, when the spring is replaced close the lid slowly and check the alignment of the locking tab, just in case this is bent and causing damage to the spring.

Bubis wrote:

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Also, is this an SM3 or an SM4? From what I have read it looks like it has the mechanics of an SM4, but the tab sets of an SM3.
I would greatly appreciate any advice.

What is the difference in the mechanics of an SM3 and an SM4 except the tab setting and clearing mechanism? (Granted, there may be minor differences made during the model production runs and cosmetic changes, but those don't change the model designation. So, apart from the tabs?)

I think bubis is spot on with the idea of an intermediate model or repairs, when these machines were manufactured we were not in a throw away society, so manufacturers would use what what was available to them and if that meant putting a later paper table etc on the machine they would do that, also there is the possibility of repairs, and Olympia etc would update the part numbers to the newer modified versions where they could to save on cost, makes perfect sense to me.