Valve Stem Cap Down the Oil Return?

So, after reading dozens of threads here, I decided to do the headgasket on my wife's 2012 prius 3.
All went well, until I bumped a rocker and the valve stem cap fell down the oil return after torquing the new headgasket on. !@#$ &*^% %!@# $%^&!!!!!!!
Has anyone here dropped anything down the oil return ports in the head?
Does it go straight to the pan?
Will boroscope here after I mentally reset, but thought someone here might have done something similar.
Will post results after FOSAR with magnets/etc.
Photo doesnt seem to upload, but its the #3 cylinder exhaust, starboard oil return I think.
Thanks.

 

Update:
3/8" (~10mm) boroscope head is just to large to fit down the oil return.
1/4" (~6.5mm) head will fit down the return and past the shelf to the oil pan.
There seems to be a shelf at ~8" from the top of the head, and the distance to the pan seems to be ~19-20".
My stem cap is at ~19-20", so if I can't get it with a small magnet retriever, I'll just have to take the pan off.

 

I did get a small boroscope down to see it @ ~19".
Most magnetic pickups were too wide to fit down the channel, so I used a coat hanger and a very small donut magnet and it came right out.
Thanks for the response, your posts have been a huge help in learning and working on these cars.
I can email photos of the special tool if anyone needs, but I cant upload photos here.

the boroscope was this:

 

Idk about running, I had mine apart and fished it out with a small ring magnet on the end of a 20AWG wire.
I didnt take my oil pan off, but if I hadnt found it with the wire, that would have been my next step.
Have you boroscoped it to see if it got caught on that shelf half way down?