You will probably have to drill the retaining pin out . But be warned when you do get the box off it is not a simple job to step down without damage or loss .There is a retaining plate that holds the springs in place to remove first . There are also two small springs tat work on the trippers that are a constant problem in so much as they can be very brittle so extra care must be taken on there removal . Don't know what your actual problem is but the there main faults are
1 broken spring
2 broken tripper spring
3 broken swivel
Also check for worn extractor legs so that they do not cock the ejectors enough to engage .
