Sorry about the confusion, I had originally put 10 Watts (close) as the original spec but changed my mind for some reason and edited it to 15 Watts.
The LH picture shows the correct uprated replacement for R751 and Malc may be right at 15/17 Watts although I always thought it was 20, . The same picture also shows R752 as the troublesome type of Osbourne manufacture, the most unreliable version of R751 was identical other than the value of course. The upgrading of R752 may not have been on a BRC technical bulletin but it certainly was in DER and possibly RR fairly late in the chassis life span and certainly a couple of years after the R751 mod was made mandatory.
If either of these went open circuit it could case major damage to multiple components and to the paxolin destroying the PCB. To be honest with the white cement types fitted in the right hand pic, R751 did fail but very rarely but I don't recall R752 of that type failing at all. I once tried an experiment on a scrap set running with R751 o/c, there certainly was quite a lot of smoke but no damage occurred to the PCB material until around the 45 minute mark.
I certainly remember those resistors shown in the 3500 board pic, they were green in colour in very early production and later grey. I don't remember any failures of that type either.
Hope this helps.