The problem with any thick opaque finish is what it may hide underneath. If corrosion has started, or starts later on, the damage can be irreparable before it is noticed. 
 I would guess that the Linseed oil varnish was originally applied by a previous collector rather than the original user, given how it would interfere with cleaning and maintenance  during it's lifetime of use.
		 
		
		
		
		
		
		
		
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