Have a look for the 400D & 400L on here too, they are almost identical to the 400H.
Looking at the manual, it lists a number of paper capacitors, these will almost certainly be leaky, some are grid coupling capacitors.
Also from experience I've had a number of the 1500uF low voltage capacitors fail open circuit, these were single cans rather than the dual can used in this, they were in a pair of 412A and another in a 5245L.
David
factory