Kit 6550 resistor failures and voltage irregularities

[Revoli]

First a huge thanks to those reading this and offering advice

I have a persistent problem with my Kit6550 amp. Before I dive in and do stuff could someone check my sanity on what planning to try??? Amp ran for many years no problems. Now symptoms as follows:

(with reference to original circuit diagrams)

Resistors R35,36,37,38 (560ohm 7W Large) overheating and failing (replaced twice).

Test Voltages are off in two cases:
a. between V4 pin 8 8.8V now versus 6.7V originally on build
b. between V3 pin 8 8.5V now versus 6.7V originally on build
c. Valves 5,6,7,8 between pins 2 and 7 now 2.6v versus 5.6V on original build

I replaced most caps and many resistors when this first happened as amp getting old and whilst in there seemed like a good idea (and suggested here). Now initial thoughts were to:

1. Check all wiring is still sound
2. Up resistors R35,36,37,38 to from 560Ohm 7W (https://uk.rs-online.com/web/p/throu...istors/2061035) to 560Ohm 14W wirewound resistors (https://www.cricklewoodelectronics.com/14W560R.html) but am wary it all worked fine on 7W resistors previously so whats changed and am I just shifting problem elsewhere???
3. Should I replace all valves as a precaution (is this good practice to periodically do before thay fail???)

I would attach circuit diagrams and the testing details for ease of reference (also has my full test results scrawled on them etc) but files too big for forum. If its helpful I can email!

Thanks in advance.