I'm relieved to hear this ended well, it sure sounded like it had the makings of something more sinister. All that said, is it just me, or does it seem like there were an awful lot of deviations from assigned heading and altitude all because of an airspeed indicator? Perhaps he was spending a lot of time trying to work out if there was an icing issue, but it seems to me, in that type of aircraft, and given his proximity to the ground, his options were limited, and given that he was already on the approach, it would've been better to concentrate on flying correctly and getting down ASAP on the approach.
I do give a lot of credit to ATC who gave him a lot of leeway and tried to head off any problems the moment they started to develop. He's very lucky that the airspace wasn't busy, or his deviations may have been cause for concern.
At the very least, we can try to put ourselves in his shoes and benefit from his experience. If this happens to me, I'll try to remember this, and focus on flying as efficiently as possible to get the plane down quickly. It's GREAT that he contacted ATC, informed them of the apparently problem, and asked to be brought down quickly. That is a very good first step.