A shame you didn't ask for advice BEFORE you replaced 'em...
Because they weren't the source of your odor.
I just replaced the toilet and holding tank in our Hunter Vision 36, 1994, and the smell is back. Not in the head but in the aft stateroom, (next to the holding tank). What could it be?
'Cuz the holding tank, unless it's leaking, is rarely if ever the source of odor INSIDE a boat because a) plastic holding tanks don't permeate and b)odor from inside the tank has only one place to go--out the tank vent. So unless the tank was leaking, there was no need to replace it.
And while dead and decaying sea life and/or stagnant sea water can create a odor IN a toilet, the odor will be confined to the head, it won't be anywhere else in the boat. And since the odor is confined to the after stateroom, that also rules out the toilet as the culprit.
The likely sources of your odors: Permeated sanitation hoses, leaking tank fitting, leaking macerator, leaking y-valve...trapped water below the sole (source is often a leaking stanchion or other deck fitting that allows water to get in between the hull and the liner...and the leak could be at the other end of the boat )...a wet bilge in SERIOUS need of a real cleaning for a change instead of just dumping in some kind of cleaner and calling it done. Or, if the tank was leaking or you had a spill when you removed it...see my last reply in "Stinkin' Overflow" in the mid-size boats forum.
So before just blindly replacing anything else, you need to find the source of the odor. It may help you to know that odors are always strongest at their source...so the best time to hunt is immediately after the boat has been closed up for a while.