Thank you for your question.
You wrote that the seller recorded the declaration of easement before the sale, so the easement is completely invalid because a person cannot create an easement in favor of himself on his own property.
"4. Extinguishment by Merger
An easement is extinguished by merger when servient and dominant tenements come into common ownership. Coast Storage Co. v. Schwartz, 55 Wn.2d 848, 351 P.2d 520 (1960). This is considered a merger of the easement into title. The policy behind merger is that an owner, whose title encompasses all the rights included within the easement, simply cannot own the same rights twice. The easement is not revived if the owner in whom it has been “merged” later conveys the land to another, unless upon express grant contained in the deed. See Radovich v. Nuzhat, 104 Wn. App. 800, 16 P.3d 687 (2001) (even if former easement was extinguished by merger, a new easement may be created by conveyance that expressly creates such easement). See also W. Stoebuck & D. Whitman, The Law of Property § 8.12 (3d ed. 2000). "
An easement appurtenant was apparently intended but my opinion is that no easement was created. He could create one now by deeding you an easement at a described location across land he still owns "for ingress, egress, and utilities" or whatever purposes you can agree on. At the moment you are usinbg this land with no easement and arguably could eventually get an easement by prescription if you keep doing to for 10 years. That is not guaranteed since you thought that you had permission to use the easement.
You bargained for a property with an easement ad the seller will have to grant one, preferably in the deed granting you the property, or, in a later deed, but the biggestr problem is that when the seller sold the adjoining parcel without a valid easement he gave up the right to grant you an easement across that parcel unless he reserved it specifically in the deed he signed granting that parcel.
The bottom line here is the easement was not properly created, as you seem to have suspected.
You can get a free consultation from some of the real estate attorneys listed by location here.
You do not want to spend more on legal fees than the parcel is worth, so please consult a local attorney and proceed with caution. I would not proceed with this purchase until the easement issue has been resolved to the point that a title insurer will be willing to insure your title including the easement.
I hope this information is helpful.