I don't know about this model, but in later Hamegs, HM203-5/-6/-7, HM605, I've found the electrolytic capacitors in the power supply (Cosonic brand) have always been troublesome, to the extent that I change them routinely. Other than that, I don't think automatically fitting new capacitors is a good idea, for most equipment. You can probably leave them alone, but if it starts to act up, check the power supplies, which is essential when troubleshooting any electronics, and don't be surprised if the capacitors need changing.
BF254A looks like a superior replacement for TIS69, which has probably been obsolete for a very long time. Makers often substituted one part for another in the course of production. Hameg weren't good at documenting changes they made. They were probably matched, because FET characteristics within a type, are notoriously variable. It's quite common to see a monolithic matched pair in that position, but this would have been an introductory scope.