Yep the TOP243Y's blue caps are X7R and "glued" with transparent PCB lacquer. And now i am not affraid of high temperature, check following:

I have made a very comprehensive upgrades and repairs.
Backplate:

Whole subwoofer backplate with all electronics was dissasembled and the outside heatsing was removed too. Removed and cleaned all degraded glue and backplate was cleaned to aluminium gloss and all glue hard remants was grinded.
All pure aluminium heat conductive surface connections was filled with heat conductive paste and the edges was glued to prevent vibrations. Between outside black aluminium heatsink and the backplate was added heat conductive paste too.

New edge sealing and bass speaker sealing was applied.

[attachmentid=9697954][attachmentid=9697955][attachmentid=9668880] [attachmentid=9668883][attachmentid=9744125]

AMP boards, APB board and I/O board:

All electrolytic caps on amplifier boards and audio processing board was replaced by ELNA RFS Silmic II and bipolars was replaced by Nichicon MUSE.

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All factory glued connectors and PCB pins was replaced by new ones and all wire contact was crimped with new contact crimps.

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Audio processing board was separated from I/O board and soldered new contact pins and headers to make it detacheable. Input cable was removed and soldered
JST-XH 8 pin header and custom cable made for connection to PSU board. New custom made signal cable from audio processing board to amp boards used.
Almost all cables was tied together with cable ties. Removed all degraded glue from I/O board and I/O connectors was resoldered with fresh solder. Replaced all JST-VH conn headers.

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PSU board:

Replaced mains power switch and grid input connector with grounding pin connected to backplate with yellow/green wire.

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Replaced all electrolytic caps for high quality ones (Nichicon, Rubycon) and the most of ceramic caps.

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[attachmentid=9744123][attachmentid=9744124]

Replaced all TO220's aluminium oxide heat conductive pads (lot of them brokes when disassembled) with heat conductive paste. Custom made linear reg / diode heatsink, shape silmiliar to IRF740 heatsink. Custom made carrying L shape heatsink. Added ribbed heatsink for better heat dissipation. (ebay sourced)

[attachmentid=9668902]

All heat sink connection surface filled with heat conductive pad sheet. All screwed together and screws was glued or transparent protective PCB lacquer lacquered to prevent unscrewing. The most important thing was connect the carrying L shape heatsink to backplate with heat conductive paste for best heat dissipation and tightened using 6 screws with self locking nut and the edges was glued.

[attachmentid=9668904][attachmentid=9697977]

Part of PCB copper pad under heatsink connection near D13 was scraped off to make it unconductive to heatsink. Heatsink side of L11 near C20 was unsoldered
and heatshrinked and glued to PCB.

[attachmentid=9668907] [attachmentid=9668911]

This makes the heatsink conductive isolated from the power supply board and the mains grounding wire can be safely connected to backplate and now can fulfill its function.

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After this upgrade the heat dissipation is much more better than original which can guarantee much much longer lifespan. In the standby mode the outer heatsink
is hand touch cold. In power on and common use the backplate and heat sink after some time are hand touch warm but not hot (about 35-40°C).
For the even better heat dissipation the outside heatsink can be equipped with FAN which can lower the temperature to lukewarm if used low rpm and low noise FAN.

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Upgraded active cooling with 140mm low noise FAN less than 20dB at full rated speed.

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Wooden case:

Wooden case all internal edges was reiforced with new glue and after then whole case was damped with wadding filling. Bassreflex pipe was removed and newly glued.

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All inside

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After this case upgrade the bass are deeper and louder about 2-3 dB compared with the wooden case with no filling. Compared both with the same master volume
and SUB volume settings.