06 Merc MA30ELH motor lock not locking so can't reverse as motor pulls up

[twr7cx]

I have a 2006 Mercury MA 30 ELH two-stroke 30HP outboard here that came on an aluminium boat purchased from a deceased estate (don't mind the spider webs, they've been cleaned up now. It started first time despite not being used for a while).
I'm having trouble with not being able to lock the motor in place resulting in an inability to reverse as the motor pulls itself upwards. I haven't been able to find a diagram of how it works or should be setup. Here's some photographs of the lock setup, linkages and springs:

But if I push it here it locks the motor in place - so perhaps something is missing or not setup correctly that should pull it this way?:

Motor details:

Any ideas or tips on what the fault could be? Anyones see anything obviously wrong or missing?

 

[twr7cx]

Found a diagram of the parts that shows the missing spring - it' shown as 22 in this diagram:



and 26 in this diagram:




There seems to be five possible part numbers/versions of Mercury Spring though:
953843 - short
24-95383 4 short
953835 Long/XL/XXL which seems to be for serial number 0N021906 and below
24-95383 5 Long/XL/XXL for serial number 0N021906 and below which according to some sources has been replaced by:
879194008 Long/XL/XXL which seems to be for serial number 0N021907 and up
Based on my serial number (0N074098) it would be this one out of the two Long/XL/XXL models. But unsure how to identify if I need the short of the long versions? Going to head in and have a chat to the local Mercury dealer, hopefully they can advise and order me in the correct part.