I found that after replacing the AirMatic pump, it's not unusual to have the rear struts very firm. Why I can't remember but on a number of occasions after replacing the pump, the rear struts would blowout during the test drive!!
And don't they go bang when they do!!
In fact, we tended to just replace struts too if the job was warranty.

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Andrew
300e 294,000mi
380sel 185,998mi
380se 309,980mi