S-VHS cassette recorders

I recently came across an old S-VHS recorder in the loft. It's many years since I had a look inside and after doing so again wondered if these were the most complex domestic devices ever designed and manufactured. This particular recorder was a JVC HR-S5000EK (rebadged in the UK as a Ferguson FR39S). I bought it as an ex-demo machine in 1991. The cassette motor inside has a date of 26 September 1988.
Some photos...
Main view after removing case:
<https://ibb.co/27FWL7j>
View after folding back main (video) board:
<https://ibb.co/T4PYj0V>
Close-up of a couple of added components on the video board (see below).
<https://ibb.co/X2bFpmS>
Some questions. Any idea what the two added "black boxes" are (one is shown in the close-up)? They are 10mm square and 4 - 5mm high, with no markings and appear to be made of hard rubber (not epoxy). This is a close-up of where one of the black boxes on the video board would appear (PCB in service manual from Elektrotanya). Basically it is above C23 and to the left of Q35.
<https://ibb.co/t3n09WF>
Another puzzle involves the added resistor under IC3 (it is on a small insulated pad. The colours aren't completely clear but it could be 18k 1%). On the board layout diagram something is shown as C178 where this resistor appears, which is under the board where IC3 is. These mods aren't shown in the service manual.
Finally, also shown on the PCB layout diagram is something designated B55 (between IC3 and the PCB?). What might this be? Unfortunately the whole service manual is an image and so not searchable. There are several other "Bnn" designations on the video and other boards, but they always seem to appear under an IC, between it and the PCB. Nothing in the "Electrical parts list" is designated "Bnn". Is it just a link of some sort?
The video recorder itself still plays back cassettes without problem, although the remote control has long since disappeared. Of course, as there are no analogue channels for it to record from it's of little use. It is, however, remarkable that 30+ years-old tapes play without apparent error, and it is even possible to read the day's text news and information (<https://en.wikipedia.org/wiki/Ceefax>) on the S-VHS cassettes.
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Jeff